The violence erupted in Kalemie, a town on Lake Tanganyika as opposition candidate Martin Fayulu was campaigning there.

It came a day after two of his supporters were killed and 43 hurt in clashes at a rally in Lubumbashi, DR Congo's second city.

A witness said "live rounds" were fired as Fayulu arrived in Kalemie.

Speaking to AFP, Rogardien Myumba, head of a federation of local NGOs, said two Fayulu supporters had been killed as they headed to greet him at the airport.

"Two opposition activists were shot dead as they were heading to the airport to welcome Mr Fayulu," he said, explaining that the police had opened fire at a barricade "to break up a crowd of Fayulu supporters."

A local doctor told AFP there were three bodies at the hospital morgue, while an emergency responder said his team had picked up four bodies.

Fayulu, 62, a little-known lawmaker and former oil executive, has made a late surge after being named the joint candidate for several opposition parties.

DR Congo is in the throes of a major campaign ahead of the December 23 election to choose a successor to President Joseph Kabila, who has ruled the vast central African country since 2001.

But the campaign has been overshadowed by fears of violence in this vast, mineral-endowed yet poverty-stricken nation.

One of Africa's most volatile countries, the DRC has never known a peaceful transition of power since independence from Belgium in 1960.

In the past 22 years, two massive wars have shaken the country, claiming millions of lives and sucking in armies from around southern and central Africa.

Lower-level conflicts are burning in the centre and east of the country which could easily flare into fully-fledged wars, analysts warn.

Kabila has remained in office as caretaker leader even though his second and final term ended nearly two years ago.

Twenty-one candidates are running to replace him.

As well as Fayulu, the front-runners are Felix Tshisekedi of the mainstream opposition Union for Democracy and Social Progress and Emmanuel Ramazani Shadary, Kabila's handpicked successor.

The violence on Tuesday in Lubumbashi, DRC's second largest city, came as Fayulu sought to attend a rally there.

He said police diverted him away from the venue, sending him to the home of a local opposition leader.

One of Fayulu's supporters is Moise Katumbi, a former governor whose power base is Lubumbashi, but who has been barred from contesting the elections.

The city, located in the southeastern province of Katanga, is also a Kabila stronghold. Shadary launched his elections campaign there on November 26.

The UN's special envoy for the DRC, Leila Zerrougui, issued a statement deploring lives lost in pre-election violence and called on the government to "take the necessary steps to avoid new incidents."

In Paris, the French foreign ministry said it was "concerned" by the violence in Lubumbashi on Tuesday, and urged the authorities to "set in place the conditions for a credible election in a peaceful climate."

In a separate development, the DRC's election commission said it had completed the deployment of voting equipment and tested it.

In a posting on Twitter, the Independent National Election Commission (CENI) said that, despite "difficulties," it could "reassure (the public) that all the election equipment has arrived across the country and in towns and, after technical verification, is in a good operational status."

The technical and logistical side of the vote has become a fierce political issue.

Some opposition parties are contesting the use of Korean-made electronic voting machines, saying the touchscreen devices can be hacked or the results manipulated.

CENI argued in return that the machines, which also provide a printout to the voter, were completely secure and the only way to quickly tally results across the DRC, a country four times the size of France but hobbled by poor infrastructure.