Residents of Haiti, waiting for nearly a week to learn the results of the presidential election, are running out of patience, and a top election official is calling for an investigation into the possibility the votes are being manipulated.

"According to me, there's a certain level of manipulation," Pierre Richard Duchemin, an electoral council member, told the Associated Press on Sunday.

Duchemin wants access to the vote counting to look into any alleged manipulation of the counting, and who may be behind it.

Supporters of Haiti presidential favourite Rene Préval demonstrate in Port-au-Prince, Sunday, Feb. 12. (AP Photo/Ariana Cubillos)

He also said "there is an effort to stop people from asking questions" about the counting process.

With a quarter of the votes left to be counted, Rene Préval leads by a wide margin, but is short of the 50 per cent plus one he would need to win outright and avoid a runoff vote in March.

Officials promised results Sunday night, but called off their announcement after thousands of protesters tried to storm the hilltop hotel where the news conference was to be held.

Saturday's protest, Préval supporters wave a flag with his photo, Port-au-Prince. (AP Photo/Ariana Cubillos)

During the day, thousands of Préval supporters danced and sang in the streets of the capital, Port-au-Prince, chanting: "We've already voted. We aren't voting again!"

Préval was president from 1996 to 2001 and is the favourite of many of Haiti's poorest people.

His backers hope he can stabilize the country and end the violence that pervades the Caribbean nation. Despite the presence of UN forces, armed gangs roam the streets and violent incidents are common.

The longer they wait, the more suspicious they get and the angrier they become.

Préval supporters claim the election has been stolen from them. Préval had a strong lead early in the vote count, but that lead has continued to slide.

Sunday's protests dwindled in the night to a single determined group. It was clear they surprised the UN soldiers guarding the hilltop, nearly overwhelming the few troops on duty. Reinforcements were caught on the other side of the demonstrators, with no other route up the hill.

The protesters went home peacefully, but vowed to return to the streets, in even bigger numbers. And they promised to be a lot less co-operative on Monday, if their candidate isn't declared the winner.