Some 300 Haitian migrants reached the United States Sunday after their wooden boat ran aground near a Florida Keys private club, local authorities said.

The packed boat beached around 1300 GMT near Ocean Reef, an upscale private club in North Key Largo, on the southern tip of Florida, said the Monroe County Sheriff's Office, cited by the Miami Herald.

"Initial reports show the (people) involved in this suspected smuggling venture are Haitian," said the US Coast Guard on Twitter.

Chief Patrol Agent Walter N. Slosar of the US Border Patrol said multiple agencies were responding to a "dangerous situation in the Florida Keys involving approximately 300 migrants... many in need of medical attention."

He said 163 of those on the boat had swum to shore, sharing a photo on Twitter of the vessel crowded with people and listing sharply to one side.

Another picture showed some 20 people wrapped in striped towels clustered on the shore, piles of what appear to be wet clothes nearby.

US Customs and Border Protection in the state announced the opening of an investigation into what it called a "maritime smuggling event."

The arrival was the third time US authorities had detained Haitian migrants trying to reach the United States in a week.

On Friday, the Coast Guard intercepted 123 people on board a small vessel off Anguilla Cay, in the western Bahamas, and last Sunday, it detained more than 140 people off the coast of Andros, the largest island in the Bahamas.

Human smugglers are known to use the Bahamas -- a group of islands near the Florida coast -- as a jumping-off point for getting people, many from other Caribbean countries such as Haiti, into the United States, in what can often be a treacherous journey.