A Bangladesh Air Force training jet has crashed into a school campus in Dhaka, the country's capital, killing at least 20 people.

Nearly all of the 31 killed when the plane crashed were children. Dozens more were being treated as the nation declared a day of mourning.

A Bangladesh Air Force training aircraft crashed into a school campus in the capital, Dhaka, shortly after takeoff on Monday, killing at least 18 people including the pilot and injuring 164 others, the military said.