TORONTO — One person is dead and five are missing after a military helicopter operating off a Canadian frigate during a NATO exercise crashed into the sea between Greece and Italy, Canadian Prime Minister Justin Trudeau said Thursday.

Mr. Trudeau said one body was found, and the five others aboard the aircraft were missing.

“We hold out hope to find the missing,” he said.

The Cyclone helicopter was deployed on board the Halifax-class frigate Fredericton and was participating in a NATO training exercise off the coast of Greece when the incident occurred, according to the Canadian Armed Forces.

Gen. Jonathan Vance, Canada’s top military official, said the ship lost contact with the crew on Wednesday evening and that flares were spotted from the water minutes later. Gen. Vance said flares would have been automatic when it ditched.