A Bangladeshi fighter jet crashed into a school in the capital Dhaka on Monday, killing at least 20 people and injuring more than 170 in the country's deadliest aviation accident in decades.

Many of the victims were young students who had just been let out of class when a Chinese-made F-7 BJI aircraft slammed into the Milestone School and College.

An AFP photographer at the scene saw fire and rescue officials taking away the injured students on stretchers, while army personnel helped clear the mangled wreckage.

More than 50 people, including children and adults, were hospitalised with burns, a doctor at the National Institute of Burn and Plastic Surgery told reporters. The incident occurred at the Milestone School and College in Dhaka's northern area of Uttara, officials said.

"Bangladesh Air Force's F-7 BGI training aircraft crashed in Uttara. The aircraft took off at 13:06 (0706 GMT)," the military's public relations department said in a statement.

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

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

Watch the video below, as shared by AFP:

"A third-grade student was brought in dead, and three others, aged 12, 14 and 40, were admitted to the hospital," said Bidhan Sarker, head of the burn unit at the Dhaka Medical College and Hospital, where some victims were taken.

Visuals 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.

Muhammad Yunus, head of Bangladesh's interim government, said"necessary measures" would be taken to investigate the cause of the accident and "ensure all kinds of assistance".

"The loss suffered by the Air Force...students, parents, teachers and staff, and others in this accident is irreparable," he said.

An 18-year-old student, Shafiur Rahman Shafi, said he heard a huge blast that felt like an earthquake.

"There were two fighter planes... Suddenly one of the two planes crashed here (in the junior playground)," he told AFP.

"It created a boom, and it felt like a quake. Then it caught fire, and the army reached the spot later," he told AFP.

The well-known private school offers education to children from kindergarten through to senior secondary.

Most of the injured were aged between eight and 14, said Mohammad Maruf Islam, joint director of Dhaka's National Burn and Plastic Surgery Institute where many victims were treated.

Grieving relatives of the victims thronged the hospital, while dozens of volunteers lined up ready to donate blood.

Tofazzal Hossain, 30, broke down in tears on learning that his young cousin had been killed.

"We frantically searched for my cousin in different hospitals," Hossain told AFP.

"He was an eighth grader at the school. Finally, we found his body."

'Deep grief and sorrow'

The military said the pilot was on a routine training mission when the jet "reportedly encountered a mechanical failure".

"The exact cause remains under investigation," it said in a statement.

The pilot tried to divert the aircraft away from densely populated areas but,"despite his best efforts", crashed into the two-storey school building, the military added.

The interim government of Muhammad Yunus announced a day of national mourning on Tuesday.

Yunus expressed"deep grief and sorrow" over the incident in a post on X.

"The loss suffered by the Air Force, the students, parents, teachers, and staff of Milestone School and College, as well as others affected by this accident, is irreparable," he said.

"This is a moment of profound pain for the nation."

The crash was the worst aviation accident in the country in several decades. The deadliest ever disaster happened in 1984 when a plane flying from Chattogram to Dhaka crashed, killing all 49 on board.

In solidarity with Dhaka

The incident comes a little over a month after an Air India plane crashed on top of a medical college hostel in neighbouring India's Ahmedabad city, killing 241 of the 242 people on board and 19 on the ground, marking the world's worst aviation disaster in a decade.

Indian Prime Minister Narendra Modi said he was"deeply shocked and saddened at the loss of lives" in Dhaka.

Relations between the neighbours have been strained since protesters in Bangladesh last year ousted leader Sheikh Hasina, an old ally of New Delhi.

"India stands in solidarity with Bangladesh and is ready to extend all possible support and assistance," Modi wrote on X.