Super typhoon Soudelor is generating waves of about 15m as it heads towards Taiwan, according to the Joint Typhoon Warning Centre.
The storm had sustained winds of 241km/h, with wind gusts of 296km/h.
Nasa snapped pictures of the storm from space.
The US space agency said the storm contained "powerful thunderstorms": "This super typhoon was generating extremely rough seas, with maximum significant wave height to [14.6m]," Nasa said. The typhoon, the most powerful of the year, is tracking over mostly open ocean but will near Japan's remote Ishigaki island today before passing over northern Taiwan.
"The storm is predicted to weaken as it continues on its trek to the west-northwest," Nasa said. "Interests in the path of this super typhoon should prepare for storm surge, heavy rainfall, mudslides in high terrain areas and typhoon-force winds."
Infrared imagery indicated the storm contained "powerful thunderstorms", with their tops recording temperatures of -63C as the air climbed, Nasa said.