At least 200 people are reported to have been killed following huge explosions at an arms dump in Congo's capital Brazzaville.
The force of the blasts was felt several miles away in the city of Kinshasa, across the border in the Democratic Republic of Congo.
Hundreds more people are reported to have been injured in the explosions.
The BBC's Thomas Hubert, in Kinshasa, says residents of east Brazzaville fled when the blasts began.
He says the explosions started shortly after 08:00 local time (07:00 GMT) and continued into the early afternoon, causing panic in both cities.
Although Congo has suffered coups and a civil war in the past, it has been largely peaceful since the 1990s.
A morgue in Brazzaville said it had counted 136 bodies - with more coming in - while a further 70 fatalities were reported by a hospital in the city, AP news agency reported.
An official in the president's office quoted by Reuters also put the death toll at about 200, citing hospital sources.
State radio, citing Defence Minister Charles Zacharie Bowao, said the explosions had been caused by a fire in the arms depot in the Regiment Blinde base in the riverside neighbourhood of Mpila.
Mr Bowao appeared on national TV to urge calm in Brazzaville and across the Congo river in 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."
Streets in the capital were littered with twisted sheets of metal and debris.
Witnesses said troops and police had sealed off the area.
Didier Boutsindi, of the presidential office, said many people were trapped in the wreckage of a collapsed church.
A worker for Congolese TV, speaking from hospital, told how he was injured amid the panic.
"I was at home and suddenly I heard this explosion coming from the camp," he said.
"There was panic. Houses and walls started collapsing and when we went outside, a wall fell on my head."
In Kinshasa, windows were blown out and roofs damaged by the blasts.
Our correspondent in Kinshasa says many people fled from the river when the explosions started, fearing shelling had broken out in Brazzaville.
China's Xinhua news agency said three Chinese workers were among those killed and several others had been injured, some seriously.
The Beijing Construction Engineering Group said about 140 Chinese workers were at a construction site near the scene of the blasts, the agency added.
Xinhua said the windows of its bureau office in Brazzaville had been blown out by the explosions.