Armed supporters of DR Congo presidential candidate Jean-Pierre Bemba carry away one of their group hurt in clashes in the capital, Kinshasa.
Police fired into the air to disperse the group, who had placed burning tyres to block streets around Mr Bemba's offices.
Gun and heavy artillery fire has been reported in the city.
Mr Bemba is trailing his rival, President Joseph Kabila, in the second round of voting. His supporters accuse the government of electoral fraud.
Mr Bemba draws his support from the western part of DR Congo, while Mr Kabila is more popular in the Swahili-speaking east.
Schoolchildren take cover from the clashes behind an armoured vehicle belonging to the UN peacekeeping force.
The government has reportedly warned it will deploy the army in the capital if Mr Bemba's supporters stay on the streets.