Fear of a coup in the small African Great Lakes nation gripped the population after a projectile landed close to the national radio broadcaster, a resident living near the affected building told AFP, requesting anonymity.

In a video seen by AFP, a tall mushroom cloud of smoke loomed over a neighbourhood in Bujumbura at nightfall, which another resident described as "spreading terror" across the city.

Very tall flames were also visible in a photo sent to AFP.

"A serious electrical accident in the ammunition store of the FDNB (Burundi National Defence Force) based in Musaga is the cause of the explosions currently being heard in the economic capital Bujumbura," Burundian army spokesman Gaspard Baratuza said.

Musaga sits in the southern suburbs of Bujumbura, the economic capital of a country ranked by the World Bank as the Earth's poorest by GDP per head in 2023.

"We urge the public to remain calm and avoid the surrounding areas; the relevant services are currently intervening," Baratuza added in a message shared in a WhatsApp group for journalists.

A resident of the Gasekebuye neighbourhood, located several kilometres from Musaga, told AFP that "the base camp is sending out munitions".

"It's munitions that are burning. They're sending bombs our way. In my house, some windows have already shattered," the resident told AFP by phone.

For years, Burundi has been gripped by a profound economic crisis, notably a three-year-long petrol shortage paralysing the country.

Since President Evariste Ndayishimiye took power in June 2020, the former Belgian colony has swung between signs of liberalising a government still in thrall to the country's powerful generals and cracking down on the opposition.

Both rights groups and the United Nations have criticised breaches of human rights in the country.