An air force training jet has slammed into a school during afternoon classes in Bangladesh, killing at least 19 people and injuring 164.

Authorities said the pilot made a “valiant effort” to divert the aircraft away from densely populated areas after encountering a mechanical failure shortly after takeoff in the capital Dhaka.

The F-7 BGI slammed into the two-storey Milestone School and College, which is attended by children aged four to 18, according to its website.

The pilot was among those killed in the incident, the military said, adding a committee had been formed to investigate its cause.

The crash is Bangladesh’s deadliest air incident in recent memory.

The ashen aftermath of the crash as rescuers search the rubble. Photo: AAP

The jet took off at 1.06pm Monday (local time) from the Bangladesh Air Force base in Kurmitola as part of a routine training mission.

Videos of the aftermath of the crash show a big fire near a lawn emitting a thick plume of smoke into the sky as crowds watch from a distance.

Firefighters sprayed water on the mangled remains of the plane. It appeared to have rammed into the side of a building, damaging iron grills and creating a gaping hole in the structure, footage filmed by Reuters showed.

Images from the scene also showed people screaming and crying as others tried to comfort them.

“When I was picking [up] my kids and went to the gate, I realised something came from behind … I heard an explosion. When I looked back, I only saw fire and smoke,” said Masud Tarik, a teacher at the school.

Head of the burns unit at Dhaka Medical College and Hospital, Bidhan Sarker, said the dead included a third-grade student and among those injured were three others, aged 12, 14 and 40.

The father of a missing student fears the worst. Photo: AAP

The country’s chief adviser Muhammad Yunus expressed his “deep grief and sorrow” in a post on X.

“This is a moment of profound pain for the nation. I pray for the speedy recovery of the injured and direct all concerned authorities, including hospitals, to address the situation with the utmost priority.”

The F-7  BGI is the final and most advanced variant in the Chinese Chengdu J-7/F-7 aircraft family, according to Jane’s Information Group.

Bangladesh signed a contract for 16 aircraft in 2011 and deliveries were completed by 2013.

The Chengdu F-7 is the licence-built version of the Soviet MiG-21.

-with AAP