A child suffering cholera symptoms is examined at the Doctors Without Borders temporary hospital in Port-au-Prince, Haiti, on Tuesday. (Emilio Morenatti/Associated Press)

Protesters in Haiti's capital are lashing out at United Nations peacekeepers and the government, blocking roads and attacking foreigners' vehicles.

Demonstrators have set up burning barricades, and Haitian police have responded with tear gas. Vehicles belonging to the UN and non-governmental organizations have been pelted with rocks.

The growing protest comes a week before national elections, and some of the demonstrators are destroying campaign posters for President Rene Preval's Unity party.

It follows days of rioting in northern Haiti over suspicions that UN soldiers introduced a cholera epidemic into the country.

The UN military mission denies responsibility for the epidemic. The number of cholera cases in Haiti is likely much higher than official figures suggest because many patients never make it to hospitals or treatment centres, a UN official said.

The Pan American Health Organization said in a statement Wednesday that 1,100 people have died and more than 18,000 people have been hospitalized since the cholera outbreak in Haiti began in late October.

But the real number of cases is "likely much larger" and better data collection is needed to track the disease as it spreads through villages and remote areas, said Nigel Fisher, the United Nations co-ordinator of humanitarian affairs in Haiti.

"I think right now what you have in terms of official figures are underestimates of the true nature of the epidemic," Fisher told CBC News.

Outbreak now in 7 of 10 regions

The outbreak has now spread to seven of the country's 10 administrative regions, known as departments, the Pan American Health Organization said.

"This epidemic is not going to go away," Fisher said, noting that experience in other countries suggests the cholera outbreak could last as long as a year. "It is almost impossible to stop."

Fisher said government agencies and relief organizations are using radio, text messages and volunteers to spread the word about how cholera is spread and how to prevent it.

A boy with cholera symptoms is carried by a relative to the St. Catherine hospital, run by Doctors Without Borders, in the Cité Soleil area of Port-au-Prince on Thursday. (Emilio Morenatti/Associated Press)

He said the number of cholera treatment centres is increasing but recent protests have been slowing the delivery of aid to some areas, particularly near Cap-Haitien, Haiti's second-largest city.

"We have had a number of protests from Haitians not wanting the centres in their communities because they fear they will somehow get infected," said. "We're trying to say having a treatment centre close is actually an advantage to you."

Fisher said the source of the cholera outbreak is not yet clear.

He said initial tests done by the U.S. Center for Disease Control and confirmed by the World Health Organization showed the cholera in Haiti was from South Asia — but didn't provide the precise origin of the strain.

"Yesterday I learned there was a French epidemiologist who, with a different methodology, is pointing more clearly at the Nepalese," he said.

He said he couldn't confirm the information, but said a group of UN officials will meet with the French epidemiologist to discuss his methodology and finding.

The UN has called for nearly $164 million US to assist with the cholera outbreak. The European Commission said Thursday that European nations should send Haiti a whole range of medical supplies, not just money, to fight the cholera outbreak.

The commission said there is a great need for medical skills, beds, epidemiological expertise, antibiotics, intravenous catheters, body bags, water purification tablets, rehydration salts and ambulances.

With files from The Associated Press