A video image taken across the Congo river in Kinshasa, Congo, on Sunday, shows a blast that rocked Brazzaville, the capital of the neighbouring Republic of Congo. (Associated Press)

Blasts rocked the capital of the Republic of Congo Sunday morning after a weapons depot caught fire, officials said, killing more than 200 people, wounding dozens and forcing thousands to flee their homes.

Another explosion struck the area in Brazzaville early in the afternoon, causing panic among those gathered there, including journalists.

The explosions shook houses in Brazzaville and echoed across the Congo River to Kinshasa, capital of the neighbouring country Congo.

Officials at hospital morgues said 206 people were killed in the blasts, while Didier Boutsindi of the presidential office said the dead included churchgoers who were killed in the debris of the collapsed building.

"Many of the faithful are trapped in the debris of the church," he said. "Several of the dead have been taken out and I confirm there are more deaths inside."

He said his uncle was killed when his home collapsed on him.

Other witnesses said the wounded may have included hundreds of Chinese workers.

Many buildings in the area had collapsed.

"It's like a tsunami passed through here," said Christine Ibata, a student.

Defence minister Charles Zacharie Boawo appeared on national television Sunday to urge calm in Brazzaville and in the neighbouring capital of Kinshasa.

"The explosions that you have heard don't mean there is a war or a coup d'etat," he said. "Nor does it mean there was a mutiny. It is an incident caused by a fire at the munitions depot. ... At this very moment our experts are there trying to extinguish this fire so this situation does not recur."

Witnesses said the explosions came from the north of the city and that the impact of the blasts threw open doors of houses in the city centre. The explosions also prompted some residents of the northern part of the city to flee south. Phone networks were quickly overloaded by calls.

Congo-Kinshasa government spokesman Lambert Mende said the blasts blew out some windows in the centre of town, but that there were no reported deaths and that the situation had returned to normal after the blasts.