The governor of Japan's southern prefecture of Okinawa has maintained his opposition to approving ground improvement work as part of a project to relocate a US air base within the prefecture.

Tamaki Denny on Monday decided to defy a high court ruling that orders the prefecture to give its go-ahead for the work at an offshore site in Henoko, Nago City.

The Fukuoka High Court has told the prefecture to approve the work by Monday.

The central government plans to relocate the US Marine Corps Futenma Air Station to the offshore site from a densely populated area in Ginowan City.

But the seabed at the planned reclamation site was found to be too soft.

The government applied for permission from the prefecture to revise its plan and carry out reinforcement work. Okinawa has not approved the revisions, and the work remains on hold.

Now that Tamaki has defied the court order, the land minister plans to take the unprecedented step of overriding a decision by local authorities to carry out the work.

Procedures are expected to start from Tuesday.

Okinawa officials will consider contesting the high court ruling by filing an appeal at the Supreme Court.

But they have no power to stop the central government from overriding their decision unless the top court rules in their favor.