Sixteen people are feared lost at sea or drowned after an old, rusting freighter grounded Friday near Miami Beach, Florida. Three died, and U.S. Customs and Border Protection took another three into custody.

According to the boat’s passengers, there were originally 40 on board, mostly undocumented immigrants from Brazil and the Dominican Republic.

The ship hit a sand bar in the shallow waters near shore and patrons of a seaside restaurant called authorities, according to the Miami Herald. Some of the passengers jumped ship, apparently trying to swim away from the rescue teams, according to the Herald. Three died, and U.S. Coast Guard unable to advance into the shallow waters.

The Coast Guard said it planned to search until dusk, and had found 24 people by midday. Authorities weren't sure if some of the passengers had made it safely to land.

"We hope they're alive," said Elee Erice, a spokeswoman for U.S. Customs and Border Protection.

It wasn't clear how the boat got into trouble, or what type of condition it was in. Officials described it as old, and said that it was 40 to 45 feet long. U.S. Coast Guard spokesman Barry Bena said he did not believe the boat sank.

Three people were hospitalized, 14 people were in custody on a Coast Guard cutter and another four were found on a beach, authorities said.

According to Reuters, the boat wrecked just off Fisher Island, the most expensive postal code in the U.S. according to Forbes magazine. The average home there reportedly sells for $3.8 million.

The boat was sailing with a Dominican Republic flag, though it was not immediately clear where it had left from and what its destination was. Erice said a handful of its inhabitants were Brazilians, and many others were believed to be from the Dominican Republic.

Click here for more from the Miami Herald.

The Associated Press contributed to this report.