American Samoa's Department of Homeland Security says strong winds and heavy rain are already battering parts of the territory as Cyclone Nisha intensifies.
The cyclone is located about 144 kilometres southeast of Tutuila with winds of about 70 kilometres per hour.
The department has issued flooding and landslide warnings, and teams are out to assist the many people still living in tents following last year's tsunami for fear they could be blown away.
Its deputy director, Jacinta Brown, says they have advised the public to take precautions.
"Those living in houses [we advise] to stay indoors and to not drive if they don't need to. A lot of the schools are closed for public and private. And those living in tents, the reason why our teams are out there is to make sure that the tents are tied down properly, to make sure that the folks don't get harmed in the course of that."
Jacinta Brown says the cyclone is expected to intensify over the next hours, before slowing down.