Doctors say the unrest in Haiti is hurting those who need help the most, after violence spread to the capital Port-au-Prince.

Aid workers, including United Nations humanitarian agencies that are structurally separate from the peacekeeping force, called for calm, saying the violence is hampering efforts to treat the tens of thousands of people stricken with cholera.

In Cap-Haitien, in the north of the country, Doctors Without Borders set up a treatment centre in an indoor gymnasium. Patients crowded the floor, intravenous bags hung from lines strung across the playing surface.

Medical workers rushed from patient to patient as a growing tide of the sick tried to make their way to the centre.

But with protesters creating roadblocks and clashing with police and UN peacekeepers, travel is difficult.

The demonstrators accuse the United Nations Stabilisation Mission in Haiti - or MINUSTAH - of bringing cholera to the island. They blame a contingent from Nepal, where cholera broke out recently.

"We came here two weeks ago and then in the beginning we had like 20 admissions a day in our cholera centre. Now the admission numbers are increasing a lot. In the last two days we have had 200 admissions per day," said Esther Sterk, a doctor with Doctors Without Borders.

More than 1,100 deaths have already been blamed on cholera.