It is noted that four patrol ships are involved in the search, but no trace of the missing plane has been found.
The disappearance near the Japanese island comes as the country aggressively bolsters its defenses in the region in response to China’s more assertive military activity in regional waters, where tensions are also rising over Taiwan.
Kyodo News reported that Japanese coast guard vessels found traces of oil and debris that could be linked to the missing helicopter, but officials declined to confirm the report.
The Ground Self-Defense Forces, or Japanese military, said the helicopter belonged to a base in Kumamoto Prefecture on Japan’s main southern island of Kyushu and was visiting Miyako Island on a surveillance mission.
Public broadcaster NHK said the helicopter disappeared from radar about an hour after taking off from its base on Miyako Island and about half an hour before it was scheduled to return.
Prime Minister Fumio Kishida said the Defense Ministry was investigating and “we will do everything possible to save their lives.”