The aircraft went missing around 4:30 pm (0730 GMT), with the Ground Self-Defense Forces scrambling to assess the situation and gather information, the official said without elaborating.

The helicopter belonged to the army's branch in the southern Kumamoto region, public broadcaster NHK said.

After taking off from Okinawa's Miyako island before 4:00 pm, it was scheduled to have returned after an hour-long flight, according to NHK.

"Saving lives is our utmost priority," Prime Minister Fumio Kishida said while briefly addressing reporters.