And the situation is likely to worsen in the next few weeks, National Army Worms Forecasting Services Centre Co-ordinator Wilfred Mushobozi has said.
"The situation is extremely grave," he said on Friday in the northern town of Arusha, the centre's headquarters.
He said about 12 000 hectares of crops had already been lost in Kiteto, in the Simanjiro District of Manyara Region.
Mushobozi said the worms were likely to reach other districts in the central, northern and southern parts of the country.
Worms have already been spotted in Babati District, the headquarters of the newly created Manyara Region in north-western
They have also been observed in urban and rural Iringa as well as the districts of Mufindi and Kilolo in the south of the country.
Mushobozi said the worms would soon "engulf" Tanzania's designate capital, Dodoma.