US authorities have suspended the search for six people aboard a medical transport aircraft that went missing on Saturday while it was travelling from Bermuda to Boston.

The Coast Guard said on Sunday evening it was ending the search off the coast of Nantucket, a Massachusetts island, after 66 hours of looking for the passengers.

"We express our deepest condolences to the families and loved ones," the Coast Guard said on Sunday.

The Federal Aviation Administration told the BBC it had lost contact with the Gulfstream G-100 plane just after 01:00 local time (05:00 GMT). Authorities have notified the next of kin of those on the flight, four Canadian nationals and two Bermudian nationals.

Authorities had said earlier that they had located a "debris field" confirmed to be from the aircraft on Saturday evening.

The plane departed from Bermuda's L.F. Wade International Airport at 23:40 local time, according to flight data from FlightAware, and was due to land at Boston's Logan International at 01:30 EDT (05:30 GMT).

According to the tail number released by the Coast Guard, the plane belonged to Latitude Air Ambulances, a company that provides international medical flights for patients returning home.

Among those on board were two pilots and two medical staff, both Canadian, Clarence Togeretz, director of flight operations at Latitude, told CBC News.

The crew flew to Bermuda to collect a patient and their relative, who are not Canadian, Togeretz said.

FlightAware's tracker shows the aircraft significantly dropped in altitude before its communications went dark, plummeting from around 7,300m (24,000ft) to 3,300m (11,000ft).

Radio transmissions shows trouble with communications between the air traffic controller and the pilot, the Boston Globe reported based on transmissions provided by LiveATC.net.

"You're coming in blind? Is that what you said?," the air traffic controller asked. "Are you declaring an emergency, or no?"

The pilot's response was inaudible.

"You're coming in a little weak so I didn't hear what your response was, if you were declaring an emergency or not," the air traffic controller said, according to the Globe.

The air traffic controller later confirmed the pilot had declared an emergency.

An area fire dispatcher asked emergency crews just after 01:00 EDT to prepare to meet a plane with an "electrical issue".

The dispatcher later said "the aircraft has lost radio and radar".