Fighting has erupted in the capital of DR Congo, Kinshasa, between government troops the militiamen supporting opposition leader Jean-Pierre Bemba.
Mr Bemba's personal armed guard are believed to number 200 men
The United Nations mission in the city says several people have been killed.
UN peacekeepers say they used armoured personnel carriers to evacuate more than 450 civilians from areas affected by the fighting.
Mr Bemba, a former rebel leader, was defeated by Joseph Kabila in landmark presidential elections last October.
The UN Security Council has expressed "serious concern" over the fighting and has called for an immediate ceasefire.
The BBC's Arnaud Zajtman, in the capital, says it is not clear who started the shooting on Thursday morning.
Gunfire continued throughout the day and, by late evening, Mr Bemba's guards controlled a large area of the city's business district.
The explosions could be heard across the Congo River in the neighbouring capital of the Republic of Congo, Brazzaville, and the city's town hall was hit by a rocket.
Eyewitnesses said they have seen the bodies of five civilians and two soldiers killed in the street battles.
UN peacekeepers said they had evacuated embassy officials, school children and injured civilians.
A spokesman for the UN mission to Congo told AFP news agency that peacekeepers were in the process of rescuing people trapped in a building in a northern district capital where fighting has been intense.
"A building was set alight this evening and some people were trapped on the higher floors. We are sending help," Didier Rancher said.
Some 15,000 UN troops - the world's largest peacekeeping force - are present in DR Congo.
On Thursday night, Mr Bemba appealed to his soldiers to return to their positions.
"I ask the soldiers of the FARDC [Congolese army] not to fire on my soldiers. We must talk like politicians," he said in a message broadcast across the city on UN radio.
Mr Bemba's personal armed guard is believed to number some 200 men, according to a 2006 estimate from the UN mission in Congo.
Last year's elections were DR Congo's first democratic elections in more than 40 years after a transitional peace process that ended a brutal five year civil war.
Mr Kabila won 58% of the vote compared to Mr Bemba's 42%. Mr Bemba contested the results, but his challenged was rejected by a court.