Congolese president Joseph Kabila casts his ballot in the country's presidential election at a polling station in Kinshasa. On December 19, The capital of Democratic Republic of Congo announced that it was barring all public rallies, four days ahead of elections in the volatile country. File picture: Jerome Delay/AP.

Kinshasa - The capital of Democratic Republic of Congo announced Wednesday that it was barring all public rallies, four days ahead of elections in the volatile country, as an opposition candidate said he had been blocked from entering the city.

The governor of Kinshasa, Andre Kimbuta, citing what he said was the likelihood of violence, announced the ban on the day that opposition hopeful Martin Fayulu was to hold a meeting in the city.

"The provincial government of Kinshasa, on security grounds, has decided to suspend election campaign activities on all of the territory of the capital from today," Kimbuta's statement said.

The ban applies to "all presidential candidates, without exception," it said, giving no details as to how long the measure would last.

"Information at our disposal confirms that in all the political camps of the main presidential candidates, extremists are prepared and are preparing for confrontations in the streets of the city of Kinshasa during election campaigning," the communique said.

The statement, which was confirmed by the Kinshasa police, said the ban would not apply to "use of media" to convey campaign messages.

Fayulu said on Twitter that the government had "prevented (him) from returning" to Kinshasa and that his motorcade had been attacked in Masinimba, east of the capital.

"What are they are afraid of?" he asked.

Police blocked the N1 highway on the city's outskirts, which Fayulu's motorcade was to take to get to the rally, and used teargas to disperse several hundred supporters who had come to greet him, an AFP reporter saw.

Hundreds of supporters also gathered in Saint-Therese Square in the Ndjili district where the rally was to take place, an AFP TV reporter said.

- Crucial vote -

More than 40 million people are eligible to cast their vote on Sunday.

The elections are a huge challenge for DRC, which has never known a peaceful transition of power since it gained independence from Belgium in 1960.

President Joseph Kabila, 47, has been in power for nearly 18 years, succeeding his assassinated father in 2001.

He is at the helm of a government that critics say is notorious for corruption, incompetence and rights abuse.

Kabila should have stepped down as president at the end of 2016 when he reached a two-term limit.

He stayed on, invoking a caretaker clause in the constitution, but at the cost of protests that were bloodily repressed.

- Front-runners -

Twenty-one candidates are vying to replace him.

The pack is led by Kabila's hand-picked successor Emmanuel Ramazani Shadary, a hardline former interior minister linked to the crackdown, and opposition leaders Fayulu and Felix Tshisekedi. 

Fayulu, 62, was a little-known legislator from a minority party who was thrust into the limelight on November 11 when opposition leaders named him their choice as a consensus candidate.

His nomination was initially backed by six other opposition leaders, including two political heavyweights -- ex-warlord Jean-Pierre Bemba and businessman Moise Katumbi, an exiled former provincial governor, both of whom were blocked from running.

But the deal swiftly fell apart as Tshisekedi, who heads the UDPS -- the country's oldest and biggest opposition party -- insisted he would take his own tilt at the presidency. 

Fayulu has repeatedly accused the authorities of trying to thwart regional campaign appearances in the sprawling country.

He said last week he had been prevented by police from reaching a rally in Lubumbashi, DRC's second largest city, and from flying to the southern mining city of Kolwezi.

Adding to political tensions is the logistical hurdle of organising the elections.

Electronic voting machines are being rolled out nationally, in defiance of opposition charges that they can be easily hacked or manipulated.

Parts of eastern DRC, meanwhile, are in the grip of militia violence and an Ebola epidemic, raising many questions about whether an orderly ballot can take place there.