North Korea has fired a missile over northern Japan in a move Japanese Prime Minister Shinzo Abe called an "unprecedented" threat to his country.
The missile, launched early on Tuesday Korean time, flew over Hokkaido island before crashing into the sea.
The UN Security Council is expected to hold an emergency meeting in response.
North Korea has conducted a flurry of missile tests recently, but this is the first time it has fired what is thought to be a ballistic weapon over Japan.
On the two previous occasions its rockets crossed Japan - in 1998 and 2009 - North Korea said they were for satellite launch vehicles, not weapons.
The BBC's Rupert Wingfield-Hayes in Tokyo says this latest launch appears to be the first of a missile powerful enough to potentially carry a nuclear warhead.
The South Korean military said the missile was fired eastward just before 06:00 local time (21:00 GMT) from near the North's capital, Pyongyang - which is rare.
Early analysis of the launch suggests the missile:
No effort was made by the Japanese to shoot down the missile but it issued a safety warning telling citizens in Hokkaido to take shelter in "a sturdy building or basement".
US and Japanese forces are currently taking part in training drills in Hokkaido.
South Korean President Moon Jae-in ordered a show of "overwhelming" force in response to the launch. Four South Korean jets staged a live bombing drill on Tuesday.
Mr Abe said he had spoken to US President Donald Trump and that both agreed to increase pressure on North Korea.
North Korea has said it is considering carrying out missile strikes on the US Pacific territory of Guam.
The report in state media, quoting an earlier military statement, came hours after President Donald Trump threatened North Korea with "fire and fury".
The North's official news agency said it was considering a plan to fire medium-to-long-range rockets at Guam, where US strategic bombers are based.
The exchanges mark a sharp rise in rhetoric between the two countries.
The UN recently approved further economic sanctions on North Korea, which Pyongyang said were a "violent violation of our sovereignty", warning the US would "pay a price".
On Wednesday, the official KCNA news agency said North Korea was "carefully examining the operational plan for making an enveloping fire at the areas around Guam" using its domestically made medium-to-long-range Hwasong-12 missiles.
The news agency reported a military statement issued on Tuesday, which probably came in response to US military drills in Guam.
In a message to the public, the governor of Guam Eddie Baza Calvo said there was currently "no threat" to the island and the Marianas archipelago, but that Guam was "prepared for any eventuality".
North Korea's statement is the latest stage in a heating up of rhetoric and tension.
Pyongyang, which has tested nuclear devices five times, launched two intercontinental ballistic missiles (ICBM) in July, claiming it now had the ability to hit the mainland US.
On Tuesday, media reports in the US claimed the North had achieved its goal of making a nuclear warhead small enough to fit inside its missiles.
While not confirmed, this was seen as one of the last obstacles to North Korea being a fully nuclear armed state.
A report in the Washington Post, citing US intelligence officials, suggested North Korea is developing nuclear weapons capable of hitting the US at a much faster rate than expected.
A Japanese government defence white paper also said the weapons programme had "advanced considerably" and that North Korea possibly now had nuclear weapons.
In response, President Trump warned North Korea to stop threatening the US, saying they would be "met with fire and fury like the world has never seen".
However veteran US Senator John McCain was sceptical about Mr Trump's statement, saying he was "not sure that President Trump is ready to act".
South Korea has proposed holding military talks with the North, after weeks of heightened tension following Pyongyang's long-range missile test.
If they were to go ahead, they would be the first high-level talks since 2015.
A senior official said talks should aim to stop "all hostile activities that raise military tension" at the fortified border between the Koreas.
South Korea's President Moon Jae-in has long signalled he wants closer engagement with the North.
North Korea has not responded to the South's proposal yet.
In a recent speech in Berlin, Mr Moon said dialogue with the North was more pressing than ever and called for a peace treaty to be signed.
He said such dialogue was crucial for those who seek the end of Pyongyang's nuclear weapons programme.
However, the North's frequent missile tests, including the most recent one of an intercontinental ballistic missile, are in consistent violation of UN resolutions and have alarmed its neighbours and the US.
South Korea's Vice Defence Minister Suh Choo-suk told a media briefing that talks could be held at Tongilgak, a North Korean building in the Panmunjom compound in the demilitarised zone between the two countries, which was used to host previous talks.
He proposed that the talks be held on 21 July, and said: "We expect a positive response from the North."
South Korea's Unification Minister Cho Myoung-gyon also urged the restoration of communication hotlines between the two Koreas, cut last year after a North Korean nuclear test.
The BBC's Karen Allen in Seoul says the ultimate aim of these talks would be to end the military confrontation that has dominated relations between the two Koreas for decades.
But it could begin with confidence-building measures such as ending the infamous loudspeaker propaganda broadcasts along the border, she says.
The Red Cross and the government have also proposed a separate meeting, aimed at discussing how to hold reunions of families separated by the Korean War, which ended in 1953.
But analysts say these could be highly fraught with Pyongyang still angry at the South's unwillingness to repatriate high-profile defectors.
The US has confirmed that North Korea tested a long-range missile which some experts believe could reach Alaska.
Secretary of State Rex Tillerson called it a "new escalation of the threat" and warned that Washington "will never accept a nuclear-armed North Korea".
Pyongyang claimed on Tuesday to have successfully tested an intercontinental ballistic missile (ICBM).
However, most experts believe that the North does not yet have long-range nuclear weapon capabilities.
In response the US and South Korea conducted a joint military exercise on Wednesday.
A statement by the two countries' militaries warned that "self-restraint, which is a choice, is all that separates armistice and war" and that their drills showed "we are able to change our choice".
The two Koreas are technically still at war as the 1950-1953 Korean War ended in an armistice.
Mr Tillerson said "global action is required to stop a global threat" and warned that any nation that provided economic or military benefits to the North, or failed to fully implement UN Security Council resolution, was "aiding and abetting a dangerous regime".
The US has asked for an urgent meeting of the UN Security Council to discuss the issue. A closed-door session of the 15-member body is expected later on Wednesday.
North Korea has fired an intermediate range missile in the direction of Japan, US military officials said.
The land-based missile was fired from near Panghyon airfield, and flew for 37 minutes before landing in the Sea of Japan, said the US Pacific Command.
Japan has lodged a protest and PM Shinzo Abe said the launch "clearly shows that the threat has grown".
Pyongyang has increased the frequency of its nuclear and missile tests in recent months, raising tensions.
South Korea said Tuesday's projectile was launched at 09:40 local time (00:40 GMT) and flew about 930km (578 miles).
The missile may have landed in waters claimed by Japan as its exclusive economic zone, according to Japanese officials.
The US said it did not pose a threat to North America.
Meanwhile Pyongyang is due to make an "important announcement" later on Tuesday, reported South Korea's Yonhap news agency.
This is the 11th detected missile launch this year, but its range seems much greater, says the BBC's Stephen Evans in Seoul.
North Korea last test-launched missiles in May. It fired projectiles on two separate occasions, both towards the Sea of Japan.
While Pyongyang has appeared to have made progress, experts believe North Korea does not have the capability to accurately target a place with an intercontinental ballistic missile or miniaturise a nuclear warhead that can fit on such a missile.
Japan's Chief Cabinet Secretary Yoshihide Suga told reporters on Tuesday: "North Korea's repeated provocations like this are absolutely unacceptable."
Mr Abe said Japan would "unite strongly" with the US and South Korea to put pressure on Pyongyang.
He added that he would call on Chinese President Xi Jinping and Russian President Vladimir Putin - who are meeting in Moscow - "to play a more constructive role".
US President Donald Trump also responded swiftly on Tuesday to the missile launch.
On his Twitter account he made apparent reference to North Korean leader Kim Jong-un, saying: "Does this guy have anything better to do with his life?"
"Hard to believe that South Korea and Japan will put up with this much longer. Perhaps China will put a heavy move on North Korea and end this nonsense once and for all!"
Mr Trump had earlier called Mr Kim a “pretty smart cookie”.
He has also repeatedly called on Mr Xi to pressure North Korea to end its nuclear and missile programmes. Beijing is Pyongyang's closest economically.
The latest missile launch comes a day after Mr Trump spoke on the phone separately with Mr Xi and Mr Abe about North Korea. The leaders reaffirmed their commitment to a denuclearised Korean Peninsula.
In South Korea, recently-elected President Moon Jae-in has called for an emergency meeting of the country's security council.
Mr Moon also met with US President Donald Trump last week, with the US leader warning Pyongyang of a “determined response”.
The US recently started setting up its controversial Terminal High-Altitude Area Defense (Thaad) system in South Korea, which is aimed at protecting against North Korean missiles.
Neighbours such as China have objected to it as they believe it undermines their security and the regional balance.
On Tuesday, Mr Xi and Mr Putin reiterated their opposition to Thaad, reported Chinese state news agency Xinhua.