An air ambulance vanished over the Atlantic early Saturday with six people aboard while flying from Bermuda to Boston, triggering a search by air and sea in the waters off Nantucket.

Air traffic control audio posted by LiveATC.net offered a fragmentary and troubling glimpse of the flight’s final communications. “Roger, you said you’re coming in blind. Is that what you said?” a controller can be heard asking the pilot. The pilot’s transmission could not be heard in the recording. The controller later confirmed the pilot was declaring an emergency just before losing contact with the plane.

The controller then asked other aircraft in the area if they showed the Gulfstream jet on their collision avoidance systems or whether they could reach them on the radio, but the medevac plane with the call sign “Heartbeat 104” was never heard from again.

The Canadian-registered air ambulance jet had four crew members and two passengers aboard when it departed Bermuda’s L.F. Wade International Airport overnight for the flight to Massachusetts, according to a statement from the Bermuda airport’s operator, Skyport.

Four of the six people on board the flight that went missing early Saturday were Canadian nationals, the country’s Minister of Transport Steven MacKinnon said on X. Transport Canada is closely monitoring and working with authorities on search and rescue efforts, he said.

The Coast Guard said the Federal Aviation Administration reported that the Gulfstream G100 had lost contact very early Saturday morning. The search for the jet included crews in the air and on the water, the Coast Guard said.

The National Transportation Safety Board said it was gathering information about the situation Saturday morning but had no further update to share.