The UN has warned it could take days for the full impact of Hurricane Matthew in Haiti to emerge, as the death toll soars to more than 800 dead.

The death toll has doubled, and may rise, as rescue teams gain access to southern areas cut off by the storm.

The World Food Programme's Carlos Veloso says some of the hard-hit towns can only be reached by air or sea.

Many of the deaths in Haiti were in the south-western coast, which suffered the full force of the hurricane this week.