Fearing a fresh escalation of the bloodshed, people in largely opposition areas have fled Bujumbura, leaving key districts that have seen some of the worst recent violence almost empty.

AFP/Nairobi

Gunmen have shot dead at least seven people in an attack on a bar in the Burundi capital, forcing them lie on the ground before executing them, government officials said Sunday.

"It was an execution... they killed seven and wounded two," said Freddy Mbonimpa, the mayor of the capital Bujumbura, adding that investigation had been launched to identify the "assassins."

The killings in the city's southern Kanyosha district took place late on Saturday, ahead of ahead of a deadline for civilians to hand over weapons, as part of a crackdown to stamp out resistance to the president.

Witnesses said the gunmen stormed into the bar -- located in a mainly opposition neighbourhood -- forcing those drinking to go outside and lie in the street before opening fire.

Burundi has been hit by waves of violence triggered by President Pierre Nkurunziza's successful bid to win a third term in office, with bodies found dumped in the streets on a nearly daily basis.

International alarm has grown as a deadline passed overnight Saturday for civilians to hand over weapons or face a new regime crackdown, drawing warnings from the head of the UN, Washington and the world's only permanent war crimes court.

Fearing a fresh escalation of the bloodshed, people in largely opposition areas have fled Bujumbura, leaving key districts that have seen some of the worst recent violence almost empty.

"They are virtually emptied of all their inhabitants who have fled because of fear from unfounded rumours of violence," Mbonimpa said.

But apart from the bar attack, the city was otherwise reported to be quiet overnight, the mayor said.

"Apart from this vile attack... the night was very quiet," Mbonimpa said.

Some 200 people have been killed in Burundi since violence broke out in April, according to the UN.

Opponents say Nkurunziza's re-election breached the terms of the Arusha peace deal that paved the way to end civil war.