Haiti's cholera outbreak death toll is likely "much higher" than reported and cases are expected to rise, the WHO said Tuesday, warning the country's multiple crises would complicate response efforts.

The crisis-wracked Caribbean nation said Sunday that at least seven people had died from cholera, raising fresh fears of a resurgent epidemic nearly three years after Haiti's last confirmed case.

Multiple suspected cases have been detected in Carrefour-Feuilles on the edge of the capital Port-au-Prince, and in the coastal neighbourhood of Cite Soleil.

The areas are entirely controlled by gangs and access to them has been very difficult since the end of July.

Conditions in Haiti have worsened in recent weeks with blockades, fuel shortages, protest marches, looting and general strikes.

"This situation greatly complicates the humanitarian response," World Health Organization spokesman Christian Lindmeier told reporters in Geneva.

"The situation is evolving rapidly, and it is possible earlier cases have been undetected."

He said the death toll figures could be "much higher".

"With the humanitarian situation as it is, the sanitary situation, and the gang-controlled areas where there's hardly any access to control, to test or even to bring in assistance, we should expect, unfortunately, cases to be higher, and to rise," he said.

Lindmeier said a request was being prepared to be submitted to the international coordination group for the procurement of oral cholera vaccines.

However, global vaccine availability is limited with demand outstripping supply.

- 'Worrying upsurge' -

Cholera is an acute diarrhoeal infection in the small intestine causing sometimes fatal dehydration. It is generally contracted from food or water contaminated with vibrio cholerae bacteria.

In February this year, Haiti celebrated three years without a single confirmed cholera case and was preparing to submit its case for cholera-free status certification at the end of 2022.

Cholera killed nearly 10,000 people in the wake of Haiti's 2010 earthquake, when United Nations workers helping with the response introduced it to the country.

The outbreak affected at least 820,000 people, the WHO said.

The first infections were detected around the Artibonite River, where UN peacekeepers had dumped fecal matter.

It was not until August 2016 that the UN officially acknowledged its role in the epidemic.

Lindmeier said there was no information yet on where the current outbreak originated, but said roughly 80 percent of people carrying vibrio cholerae could be asymptomatic, making it difficult to detect.

The United Nations said it stood ready to deploy emergency response teams as soon as safe access is assured and fuel supplies are unblocked.

On Friday the WHO warned that after years of decline, the world was now witnessing a "worrying upsurge" in cholera outbreaks.

In the first nine months of this year alone, 26 countries have reported cholera outbreaks, the WHO said.