A series of large explosions in an arms depot rocked Brazzaville, the capital of Congo Republic, on Sunday, killing at least four people, injuring dozens and sending a plume of smoke above the city.

Panic spread to Kinshasa, across the Congo River which separates the oil-producing former French colony from the larger Democratic Republic of Congo, where windows were shattered by the force of the blasts.

Both governments called for calm and there was no immediate suspicion of anything but an accident. Congo Republic is one of sub-Saharan Africa's top oil producers.

Lots of buildings have been destroyed ... There are four dead and nearly 60 injured, some seriously, Betu Bangana, head of protocol in the president's office in Brazzaville, told Reuters by telephone.

Citing Defence Minister Charles Zacharie Bowao, state radio in Congo Republic said the explosions had been caused by a fire in the arms depot in the Regiment Blinde base in the riverside Mpila neighbourhood.

China's Xinhua news agency cited Chinese officials as saying three Chinese workers were killed and dozens were injured in the explosion.

RESIDENTS FLEE

A Reuters witness in Brazzaville said residents had 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.

Fleeing residents said houses in the area had been flattened.

I saw someone being carried to hospital with their intestines hanging out. They had been hit by a shell, one witness told Reuters as he was leaving the blast zone.

Congolese TV showed pictures of panic-stricken people on the streets of neighbourhoods close to where the explosions occurred. There were also images of many injured people being rushed to hospital or being given first aid on the streets.

There were also pictures of crowded hospitals where doctors said they were selecting those who were seriously injured to have immediate surgery.

Congolese TV has also been repeating an appeal by health authorities urging all medical personnel living in Brazzaville to rush to hospitals in the city.

Mass in the Brazzaville's cathedral, about 4 kms (2.5 miles) away, was cut short as the building shook.

I heard at least five or six good sized explosions, which blew out the windows and brought down half the ceiling in our hotel, Patrick Mair, an analyst with Control Risks currently in Brazzaville, told Reuters.

The main blasts were followed by a series of smaller ones. Hours after the main explosions, a plume of grey smoke still hung over the city, a Reuters witness in Kinshasa said.

Some windows in the city were shattered by the explosions.

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.

Bangana said Sassou-Nguesso was not hurt in Sunday's explosions.

(Writing by David Lewis; Editing by Sophie Hares)