Super Typhoon Sinlaku is expected to make landfall on Tuesday in the Northern Mariana Islands and bring destructive winds, widespread heavy rain and flooding, the National Weather Service said Monday.
Power outages on the islands could be lengthy, forecasters warned.
Guam, a United States territory with US military installations and about 170,000 residents, also could see damaging winds and is under a tropical storm warning.
The Coast Guard issued flood and high wind warnings over the weekend.
The tropical typhoon — the strongest on Earth so far this year — was producing sustained winds of 278km/h on Monday as it neared the islands of Rota, Tinian and Saipan, according to the Joint Typhoon Warning Center.
While it is expected to weaken slightly over the next few days, Sinlaku should cross near the islands as a category 4 or 5 typhoon.
About 50,000 people live on the three islands, with most on Saipan, known for its laid-back resorts, snorkelling, and golf as well as the capital of the Northern Mariana Islands.
Saipan was the site of one of World War II's bloodiest battles in the Pacific, in which more than 50,000 Japanese and American soldiers and local civilians died.
President Donald Trump on Saturday approved emergency disaster declarations for Guam and the Northern Mariana Islands, allowing for additional help with emergency services.
A super typhoon is a name given to the strongest tropical cyclones that brew in the northwestern Pacific Ocean, where Earth's most intense storms usually form.
Monitored by the Joint Typhoon Warning Center in Guam, super typhoons are the equivalent of category 4 or 5 hurricanes in the Atlantic, with winds of at least 240km/h.
There have been more than 300 super typhoons identified since the warning centre started using that name nearly 80 years ago.
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