Washington - Tropical Storm Fay struck the Florida Keys Monday afternoon and was expected to take a path across the southern US state after earlier leaving more than 50 people dead on the Caribbean island nation of Haiti.

Fay's centre reached the historical resort town of Key West around 2100 GMT, bringing high storm tides, strong winds and heavy rain, forecasters said. The island, which is the at the southern tip of the continental United States, had caused flooding and at least one tornado may have touched down, the Key West Citizen newspaper reported online.

The storm was forecast to strengthen into a hurricane as it neared the south-western coast of mainland Florida, where it could strike Tuesday near Naples. The National Hurricane Centre in Miami had placed the area under a hurricane warning, and other communities on both sides of the peninsula were under a tropical storm warning.

Fay earlier crossed over Cuba. US forecasters said 10 to 20 centimetres of rain could there, prompting flash floods and mud slides. There had been no reports of the extent of the damages on the communist island.

In Haiti, a lorry carrying more than 70 passengers was swept off a road into a river, and only 25 people were believed to have survived the accident, local media reported. Seven other people had died in flooding and landslides.

Four people were killed by the storm in the neighbouring Dominican Republic.

The storm's winds were reaching speeds of 95 kilometres per hour.

Fay could dump 10 to 20 centimetres of rain in Florida and 7 to 13 centimetres of rain in the Bahamas.

The US disaster agency was prepared to respond to the storm and was working with local authorities, the White House said.