(CNN) -- A second person died Tuesday, hours after being rescued from a fishing boat that sank off the New Jersey coast, a U.S. Coast Guard spokesman said.
Four others who were aboard the boat remain missing, said the spokesman, Petty Officer Chris McLaughlin.
The Lady Mary, a 71-foot-long fishing vessel with seven people aboard, sank early Tuesday morning about 65 miles (105 kilometers) southeast of Cape May, at the southern tip of New Jersey, McLaughlin said.
He said the Coast Guard began searching for the boat's passengers around 7:45 a.m. ET.
Three people were recovered, one of whom was dead, McLaughlin said. A second rescued person died hours later, according to McLaughlin.
Their identities were not released.
The third, whom McLaughlin identified as Jose Ariese, was treated and released from AtlantiCare Regional Medical Centre, hospital spokeswoman Jenna Dearth said.
The Coast Guard said in a written statement that it had picked up an emergency "position-indicating radio beacon" about 7:30 a.m. Citing a survivor, it said the boat sank around 5 a.m. ET, three hours before the three were recovered.
It was not immediately clear what caused the boat to sink.
Cape May is about 40 miles southwest of Atlantic City, New Jersey.
CNN's Ekin Middleton contributed to this report.