At least four people died after gunmen attacked polling stations in the second city, Lubumbashi, officials say.

It is the second elections since the end of civil war eight years ago, in which four million people died.

Both President Joseph Kabila, 40, who has been in power for 10 years, and the veteran opposition leader, Etienne Tshisekedi, 78, said they were confident of victory.

In the opposition stronghold of West Kasai, polling stations were reportedly set on fire by voters angry at long delays. In the same province, there were unconfirmed reports of ballot boxes being full as polling opened.

A heavy police presence helped ensure the capital, Kinshasa was generally peaceful during the day, but after nightfall, there were numerous reports of shooting.

In other parts of the country, the governing party accused the opposition of fraud.

About 22,000 UN peacekeepers are stationed around the country - they are expected to help prevent any outbreaks of violence.