Congolese police fired tear gas to disperse opposition supporters demanding free elections on Tuesday as a US think-tank said Kinshasa must take action to ensure the upcoming vote is credible.

Activists linked to the opposition Union for Democracy and Social Progress (UPDS) party tried to rally in central Kinshasa, brandishing a banner calling for the November 28 election to be "free" and "transparent."

Dozens of police descended and fired tear gas on the protesters before pursuing them down a main street.

Police then beat several demonstrators with clubs and batons, injuring several while arresting dozens, an AFP journalist said.

"We have already counted more than a dozen of our activists who were arrested, many injured, including leaders of political parties," UPDS Secretary General Jacquemain Shabani told journalists.

He said there would be another demonstration next Thursday, beginning at the same central Kinshasa location.

Police had dispersed three previous marches in a similar fashion, including one on October 6 outside UDPS party headquarters where police fired live rounds in the air and used tear gas while arresting eight people.

UPDS leader Etienne Tshisekedi, a prime minister during dictator Mobutu Sese Seko's regime is a candidate in the election also being contested by incumbent president Joseph Kabila.

"There are serious threats to holding the election on Nov. 28 that must be addressed now," said David Pottie of The Carter Center in a report released this week.

The Atlanta-based think-tank founded by former US president Jimmy Carter urged the Congolese government to "take rapid and convincing steps to ensure the transparency and credibility of the voter register."

The group "also noted that serious incidents of intimidation and violence have occurred during campaigning", and said political players must be conscience of the potential consequences of a flawed election.

"The DRC is a large and fractured country with a violent past and present; failure to recognize this context, or worse, to exploit it for electoral gain, will undermine the possibility of genuine democratic elections," the group said.

The Carter Center based its report on information collected by observers deployed in DR Congo since August.