Over 300 people were killed and more than 1,800 injured as a devastating earthquake struck the Caribbean nation of Haiti on Saturday.

The 7.2-magnitude quake hit the western part of the country bringing down buildings including churches and hotels.

The prime minister said there was "extensive damage" and declared a month-long state of emergency.

The epicentre of the earthquake was about 12 km from the town of Saint-Louis du Sud, the US Geological Survey (USGS) said.

Haiti Prime Minister Ariel Henry said he had mobilised a team to work on the relief effort.

"The most important thing is to recover as many survivors as possible under the rubble. We have learned that the local hospitals are overwhelmed with wounded, fractured people," BBC quoted him as saying.

US President Joe Biden has authorised an "immediate US response" to help Haiti and said USAID would work to support efforts to "assess the damage and assist efforts to recover those who were injured and those who must now rebuild".

"In what is already a challenging time for the people of Haiti, I am saddened by the devastating earthquake," he said.

Haiti is still recovering from a devastating 2010 earthquake.

The USGS earlier warned that the earthquake could result in thousands of fatalities and injuries. It also said several aftershocks had been felt in the region, including one measuring 5.8 magnitude.

Frantz Duval, editor-in-chief of Haiti's Le Nouvelliste newspaper, tweeted that two hotels were among the buildings destroyed in the town of Les Cayes. He said the local hospital was overwhelmed.