Crews stopped searching late this afternoon for a 41-year-old man who has been missing since he fell overboard from the Provincetown II ferry during a country music-themed cruise in Boston Harbor Saturday night, officials said.

The Coast Guard and other agencies were searching the waters around Castle Island, extending to Deer Island, Coast Guard spokesman Ross Ruddell said Sunday afternoon.

At approximately 10:45 p.m. Saturday, the Coast Guard Sector Boston was notified by the boat’s crew that the man had fallen from the third deck into the water near Castle Island in South Boston, according to a statement from the Coast Guard.

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The man, who was aboard the ship with his girlfriend, was apparently trying to climb the ship’s third deck railing when he fell, according to a statement from Bay State Cruise Company, which operates the Provincetown II.

Interviews with passengers appear “to indicate that the gentleman had been engaging in horseplay when he fell from the vessel,” the company said in its statement. “Two passengers ... reported trying to grab at the man to stop him from an athletic leap, scaling up the ship’s railings.”

A member of the ship’s crew was 10 to 15 feet away from the man and also tried in vain to stop the man from rambling up the railing, the company said.

The man has not been publicly identified.

Crew members were positioned as lookouts as per the ship’s man-overboard rescue procedure, but no one saw him come to water’s surface, the statement said. For that reason, crews began a search operation rather than a retrieval, according to a statement from the company.

The ferry was traveling at 5 miles per hour when the man fell into the harbor, and was carrying 370 passengers and 21 crew members, according to the company.

“The deep sadness that an event like this evokes in us and our crew is indescribable,” said Mike Glasfeld, owner of the Bay State Cruise Company in a statement. “Our hearts and blessings are with those close to the gentleman who has gone missing. We are moved beyond words by the emotions of the event. There are no words to adequately describe our sympathies.”

Five Coast Guard ships — one cutter and four smaller vessels — and a Jayhawk helicopter assisted in the search, Ruddell said. The waters of Boston Harbor were 65 degrees and calm, the Coast Guard said.

“We are using a variety of Coast Guard, State and local agencies in the search,” said Commander Sean Carroll, the search and rescue mission coordinator at Sector Boston. “This is a significant, multi-agency effort.”

Boston Police and Fire Departments, Boston Harbor Police, Quincy Police Department, Massachusetts State Police, and MassPort Fire Department were all involved.

The Provincetown II has the capacity to accommodate up to 1,100 passengers, according to the Bay State Cruise Company’s website. Its weekend music cruises are marketed on the company’s Facebook page as “the wildest, largest parties on the water.”