Around 200 people were killed when an arms dump exploded in Brazzaville, capital of the Congo Republic, a senior official in the presidency said.
Hundreds more were injured by the blasts which flattened houses near the scene and sent a plume of smoke high above the city.
Defence Minister Charles Zacharie Bowao dismissed any talk of a coup attempt or mutiny, and told state radio that the explosions had been caused by a fire in the arms depot in the Regiment Blinde base in the Mpila neighbourhood.
Panic also spread to Kinshasa, across the Congo River which separates the former French colony from the larger Democratic Republic of Congo, where windows were shattered by the force of the blasts up to 4km away.
China's Xinhua news agency cited Chinese officials as saying three Chinese workers were killed by the explosion and dozens were injured, some in serious condition.
Xinhua said the dead and injured were part of a group of about 140 Chinese workers from the Beijing Construction Engineering Group.
A witness in Brazzaville said residents fled the blast area, which is near a heavily populated neighbourhood and was blocked off by the security forces as a military helicopter flew overhead.
Congolese television showed pictures of panic-stricken people on the streets of nearby neighbourhoods. There were also images of many injured people being rushed to hospital or being given first aid on the street.
Congo Republic has suffered coups and a civil war since independence from France. It has been mostly peaceful, however, since President Denis Sassou-Nguesso took power in a coup in 1997.
