Trump has approved emergency help for Guam and the Northern Mariana Islands, where Sinlakua is expected to make landfall on Tuesday
Power cuts on the islands could be lengthy, forecasters warned.
The tropical typhoon – the strongest on Earth so far this year – was producing sustained winds of 278km/h (173mph) on Monday as it neared the islands of Rota, Tinian and Saipan, according to the Joint Typhoon Warning Centre.
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.
