A major earthquake with a magnitude of 7.2 has struck western Haiti, as people fled their homes fearing that buildings might collapse.

The quake struck 8km (five miles) from the town of Petit Trou de Nippes, about 150km (93 miles) west of the capital Port-au-Prince, at a depth of 10km, the US Geological Survey said.

The United States Geological Survey issued a red alert for fatalities from the quake and said the disaster is "likely widespread".

The US Tsunami Warning System reported the threat of a tsunami in Haiti has now passed.

People in the capital of Port-au-Prince felt the tremor and many rushed into the streets in fear.

Haiti's Civil Protection service said on Twitter there were initial reports of likely casualties from its teams.

The Caribbean country is still recovering from a magnitude 7 earthquake closer to the capital 11 years ago that killed tens of thousands of people and flattened buildings, leaving many homeless.

"In my neighborhood, I heard people screaming. They were flying outside," said Port-au-Prince resident Sephora Pierre Louis, adding she was still in a state of shock.

"At least they know to go outside. In 2010, they didn't know what to do. People are still outside in the street."

Naomi Verneus, a 34-year-old resident, said she was jolted awake by the earthquake, with her bed was shaking.

"I woke up and didn't have time to put my shoes on. We lived the 2010 earthquake and all I could do was run. I later remembered my two kids and my mother were still inside.

"My neighbor went in and told them to get out. We ran to the street," Verneus said.

Tropical Storm Grace is forecasted to reach Haiti late Monday night or early Tuesday morning.