A powerful super typhoon is threatening Japan's Okinawa islands with violent winds and torrential rains, and has forced the US air force base to move some of its aircraft.

Neoguri intensified on Monday to the equivalent of a Category 4 hurricane over the Pacific Ocean and was expected to hit Okinawa early on Tuesday before reaching mainland Japan on Wednesday, the national weather agency said on Monday.

Al Jazeera meteorologist Steff Gaulter said Neoguri is likely intensify to the equivalent of a Category 5 hurricane, the most powerful category, before it reaches Okinawa.

The US Kadena Air Force base in Okinawa began evacuating some of its aircraft on Sunday in preparation. One official described the storm as "the most powerful typhoon forecast to hit the island in 15 years".

The meteorological agency forecast Neoguri - raccoon in Korean - would dump up to 80mm of rain an hour on Okinawa.

The storm was then expected to head north and slam into the Japanese mainland. The storm was expected to be downgraded by the time it hit Kyushu, but is still likely to cause major damage.

"I'm calling on the heads of municipalities not to hesitate in issuing evacuation warnings and don't be afraid of being overcautious," Keiji Furuya, the state minister in charge of disaster management, told a government meeting.

Okinawa is regularly hit by typhoons but islanders were taking no chances with fishermen on Miyako island bringing boats back to port and tying them down with ropes.