The competing claims follow a disorderly election day on Sunday in which many Congolese were unable to vote due to an Ebola outbreak, conflict and logistical problems.

The vote is meant to choose a successor to outgoing President Joseph Kabila after 18 years in power and could lead to the vast central African country's first ever democratic transition.

Any disputed outcome could lead to a repeat of the violence that followed the 2006 and 2011 elections and a wider security breakdown, particularly along Congo's borders with Rwanda, Uganda and Burundi, where dozens of armed militia are active.

Vital Kamerhe, the campaign manager to opposition candidate Felix Tshisekedi, said early counting showed Tshisekedi and the other main opposition candidate Martin Fayulu neck-and-neck, both with over 40 per cent of the vote.

He said ruling coalition candidate, Emmanuel Ramazani Shadary, who is backed by Kabila, had only about 13 per cent, although a significant part of the vote remained to be tabulated.

The election is a first-past-the-post system with no run-off.

Nehemie Mwilanya, Kabila's chief of staff and a member of Shadary's campaign, told a news conference on Monday morning he was confident Shadary had won, although he didn't provide specific figures.

"For us, victory is certain," Mwilanya said.

Fayulu's camp has not yet provided numbers but Fayulu said late on Sunday Shadary's camp was "dreaming".

The most recent poll before the election showed Fayulu, a former Exxon Mobil manager, leading the race on 47 per cent. Tshisekedi had 24 per cent and Shadary 19.

The first partial results are expected from the national electoral commission on Tuesday.

Election day was mostly peaceful despite several violent incidents, including an altercation at a polling place in eastern Congo in which at least three people were killed.

Australian Associated Press