The 7.2-magnitude quake hit the west of the country on Saturday morning, toppling and damaging buildings including churches and hotels.
The prime minister said there was "extensive damage" and declared a month-long state of emergency.
Haiti is still recovering from a devastating 2010 earthquake.
The epicentre of Saturday's quake was about 12km (7.5 miles) from the town of Saint-Louis du Sud, the US Geological Survey (USGS) said.
The tremor was felt in the densely-populated capital of Port-au-Prince, some 125km away, and in neighbouring countries.
"Lots of homes are destroyed, people are dead and some are at the hospital," Christella Saint Hilaire, who lives near the epicentre, told AFP news agency.