Hurricane Matthew has brought the worst humanitarian crisis to Haiti since the 2010 earthquake, the United Nations has said. 

Winds up to 230 kilometres an hour and heavy rain created what's being called a catastrophic situation in places like Les Cayes.

Up to a metre of rain was predicted, threatening mudslides and flash floods.

Communications are down across most of the country and there is no immediate information on casualties and the extent of the damage.

The interior minister says damage to homes and crops is likely to be extensive.

Tens of thousands of people in Haiti are still living in flimsy tents and makeshift houses following the quake six years ago from which it's still struggling to recover.

The U.S. has already offered the use of some of its helicopters to help with relief efforts.

The hurricane's expected to reach the Bahamas, Florida and the Atlantic coast of the southern US today and tomorrow.