SANTIAGO, Chile－Chile's air force lost radio contact with a transport plane carrying 38 people on a flight on Monday evening to the country's base in Antarctica, and authorities indicated several hours later that they were not optimistic about the aircraft's fate.

On Tuesday, the military said the cargo plane "must have crashed" given the number of hours it had been missing, adding that a rescue team was searching for survivors.

The C-130 Hercules carried 17 crew members and 21 passengers, including three civilians. The personnel were to check on a floating fuel supply line and other equipment at the Chilean base.

Chilean President Sebastian Pinera said he was with his defense and interior ministers at the air force headquarters monitoring developments.

In a statement, the air force said the plane had not been heard from in more than seven hours and likely would have run out of fuel around 12:40 am.

The air force "will continue the search... in order to rescue potential survivors", the statement said.

The plane took off at 4:53 pm from the Chabunco Air Base in the southern city of Punta Arenas, which is more than 3,000 kilometers from the capital of Santiago. Contact was lost at 6:13 pm, the initial announcement said.

Drake's Passage, where the plane was missing, is infamous for severe weather conditions, including freezing temperatures and ferocious storms. But the air force said late on Monday that the weather was good when the plane began its flight, or the mission would not have been carried out.

General Eduardo Mosqueira of the Fourth Air Brigade said a search was underway and a ship was in the general area where the plane should have been when contact was lost.

Mosqueira said the aircraft would have been about halfway to the Antarctic base when it lost contact. No emergency signals had been activated, he said.

He said the plane, whose pilot had extensive experience, had been scheduled to return on Monday night.