“We count at least 150 dead in the military hospitals and around 1,500 injured, some of them seriously,” the diplomat said when contacted by telephone from Paris, after explosions rocked the Mpila military barracks in the east of the capital.
AFP correspondents in Brazzaville had earlier reported seeing four bodies, including that of a young girl, in a clinic near the barracks, while the Chinese Xinhua news agency said three Chinese workers were killed and dozens injured in the blasts.
A number of wounded, many wearing military uniforms, were also seen receiving first aid in the streets, an AFP correspondent said.
The blasts, which even blew out windows across the Congo River in Kinshasa, were set off by a blaze in two munition depots in the Mpila armoured brigade barracks, in the east of Brazzaville, according to soldiers who refused to be named.
A diplomat told AFP the incident “is not political and the president (Sassou Nguesso) is with the chief-of-staff to coordinate operations”.
There was no official word from the government on the cause of the explosions, or damage sustained.
A diplomat said firefighters were finding it hard to fight the blaze because of ongoing explosions.
A number of houses were completely destroyed, while others saw windows and doors were blown away and roofs lifted, an AFP correspondent said.
A Catholic church, close to the barracks, was also damaged when the explosions occurred during Sunday mass.
“It’s a munitions depot that caught fire in Mpila. That’s next to the presidential palace. I saw two people injured. One had a leg injury, the other a wound to the shoulder,” a woman living in Brazzaville told AFP.
“They had probably been hurt by falling debris from houses. A wall fell down in my home,” she added.
“There are many people on the street. They are running away, barefoot, carrying parcels on their heads. Some are hardly dresssed. There are no cars, no buses, no taxis,” she added.
River traffic between Kinshasa and Brazzaville was also suspended, a Kinshasa port official said.
Xinhua news agency said some 140 Chinese workers from the Beijing Construction Engineering Group were working near the munitions depot when the blasts occurred.
The dormitory building of China’s Huawei company was badly damaged, but there were no casualties reported there, Chinese officials said.
At least five strong explosions were heard between 8:00 am (0700 GMT) and 10:45 am (0945 GMT).
A plume of smoke could be seen over Brazzaville from across the Congo River in Kinshasa, capital of neighbouring Democratic Republic of Congo.
In addition to the blasts, there were other weaker detonations which continued into the late morning.
On the opposite river bank, in Kinshasa, several buildings had their windows blown out, and a church in the centre of town also suffered damage, a cleric said.