Protesters demanded the United States and Japan immediately scrap plans to deploy 12 MV-22 Ospreys at the Futenma US base on Okinawa and shut down the Futenma base in the crowded city of Ginowan.
The turnout at the main rally was estimated by organisers at more than 100,000. Okinawan media put the number at “tens of thousands”.
“We don’t want the Osprey, the world’s most dangerous aircraft” read a placard at the mass rally at a seaside park near the base, according to television footage. “Osprey. No!” said another.
Similar rallies were staged on two smaller islands in the Okinawa island chain and in Tokyo several thousand people circled the Japanese parliament building.
The Osprey has rotors that allow it to take off like a helicopter. It can refuel in the air, allowing it to cover big distances in a region where concerns have mounted over the rise of China.
Ginowan mayor Atsushi Sakima told the rally the safety of the hybrid transport aircraft “has not been guaranteed”.
In April, an MV-22 Osprey crashed in Morocco, killing two Marines.
Another variant of the aircraft crashed in June in Florida, injuring five crew members, although US officials said the accident was not due to mechanical problems.
Concerns heightened further when an MV-22 made an emergency landing in a residential area outside a Marine base in Jacksonville, North Carolina, on Thursday.
Japanese Prime Minister Yoshihiko Noda told US Secretary of State Hillary Clinton of Japan’s concerns over the Osprey’s safety on the sidelines of an Asia-Pacific summit in Russia on Saturday, according to Japanese media.
A series of crimes committed by US troops over the years, including the 1995 gang rape of an Okinawan schoolgirl, have fuelled resentment among islanders against the heavy US military presence.
The United States and Japan have been bogged down for years in talks to relocate the Futenma base, which locals want to see moved away from the island chain.