TOKYO — With the threat of a mass protest, the governor of Okinawa on Sunday rejected a US plan to deploy Osprey military aircraft on the sub-tropic Japanese island chain amid safety concerns.

"We have no choice but to reject it if they forcibly bring in something which is questioned over its safety," Okinawa governor Hirokazu Nakaima told Japanese Defence Minister Satoshi Morimoto, according to Japanese media.

Nakaima and Morimoto met at the governor's office in the main Okinawan city Naha, reports said, as about 220 people held a rally outside in protest over the continued US presence on the island.

Although local governments in Japan have no legal grounds to reject a US deployment plan, strong resentment from Okianwan islanders could further erode public support for the government of Prime Minister Yoshihiko Noda.

On Friday, Washington had formally informed Tokyo it would go ahead with the planned deployment of Osprey at the marine corps airbase of Futenma near Naha in October.

"If the United States forces through the Osprey deployment and an accident or other incident occurs in a densely populated area, it will lead to a movement demanding immediate shutdown of all bases," Nakaima told reporters.

The aircraft was plagued with problems in its early years in the 1990s, but US officials say the technical glitches have been cleared up and the US Marine Corps says it has proven invaluable.

The Osprey is a hybrid aircraft with rotors that allow it to take off like a helicopter and engines that can tilt forward, enabling it to fly like an airplane at greater speed than a chopper.

The Futenma base where the aircraft is due to be deployed has been at the centre of a long-running stand-off as it sits in a developing urban area.

A huge US military presence in Okinawa, accounting for around half of the 47,000 troops Washington has in Japan, has angered islanders there.