HONG KONG — Malaysia Airlines announced Saturday morning that it had lost contact five hours earlier with one of its flights, which was carrying at least 239 people to Beijing from Kuala Lumpur, and had activated a search-and-rescue team.

The plane, a Boeing 777-200 operating as Flight MH370, took off at 12:41 a.m. Air traffic control in Subang, a suburb of Kuala Lumpur, lost contact with the plane almost two hours later, at 2:40 a.m. The plane was scheduled to land at 6:30 a.m. in Beijing, but there was no further word on its fate by early Saturday afternoon.

Vietnamese officials told local news media that the aircraft had never reached the air traffic control region for Ho Chi Minh City, formerly Saigon, after the plane was supposed to have passed over the ocean between northern Malaysia and southernmost Vietnam.