UN peacekeepers in the Democratic Republic of Congo have rescued several foreign ambassadors trapped in a house in Kinshasa by heavy shooting.
Smoke was seen rising from Mr Bemba's residence
The diplomats were meeting opposition leader Jean-Pierre Bemba in his house when a gunfight broke out.
The group included the UK envoy and the head of the UN mission, the UN said.
The incident follows clashes on Sunday between forces loyal to President Joseph Kabila and Jean-Pierre Bemba, who face a run-off election in October.
"They're out and they're coming to UN headquarters. Everyone's safe," a spokesman for the UN force said, after the diplomats were rescued.
In July's first-round of voting for a new president, Mr Kabila took 45% of the vote, just short of the 50% needed for victory, while Mr Bemba gained 20%.
Witnesses told Reuters news agency that in Monday's violence, President Kabila's presidential guards opened fire on the house using tanks and heavy machine guns, Reuters reported.
Presidential guard troops have been patrolling Kinshasa's streets
Mr Bemba's party said the violence was an attack on the presidential challenger's life, but a senior military official said Mr Bemba's guards had provoked the battle, the Associated Press reported.
Mr Bemba is a former rebel leader and retains his own personal security force.
A diplomatic source told AFP the fighting had lasted at least half-an-hour, and had destroyed Mr Bemba's helicopter.
The diplomats were rescued by a convoy of armoured vehicles in a joint operation by at least 250 European and UN peacekeepers.
The centre of the capital, Kinshasa, was deserted all day following Sunday's clashes in which, according to the UN, five people died.
The BBC's Said Penda in the city says shops and offices were closed and there were few buses or taxis, as people were afraid to go to work.
A senior official from the Independent Electoral Commission told the BBC he had been unable to get to work because of sporadic shooting.
He said the same was true for his colleagues, which is why the CEI website had not been updated to show the nationwide results.
After the election results were declared, Mr Kabila appeared on state TV, saying he had won a "great victory".
On Sunday, UN Secretary General Kofi Annan urged all "candidates to abide by the electoral law in the resolution of any disputes related to the electoral process," and urged them to "accept and respect the final results of the elections, in a spirit of peace and reconciliation."
The 30 July election was the first democratic poll to be held in the country since it gained independence in 1960 and follows the official end of a five-year conflict.
Turn-out was about 70% of the 25m registered voters.
The results show a regional division in DR Congo, a country two-thirds the size of western Europe.
Mr Bemba won most votes in the west of the country, while Mr Kabila gained most support in the Swahili-speaking east.
The polls are meant to put an end to a transition process established after five years of war that ended in 2003.