American Samoa and neighbouring Samoa were expected to miss the heart of the powerful storm but were taking a pounding from torrential rain, gale-force winds and flooding.

The Samoa Meteorology Division warned of squally thunder storms and isolated flooding, with an anticipated high surf surge up to eight metres high.

"Very destructive" winds of 95-130 kilometres per hour (60-80mph) with gusts up to 169kmh were forecast to hit the main island of Savai'i.

At Poloa in American Samoa, a family of four managed to pack two suitcases of belongings before fleeing as their beach house was washed away.

Three people were washed out to sea at Fagasa, but managed to make it safely back to shore as families in coastal areas were advised to move to higher ground with the situation expected to worsen.

Pago Pago International Airport in American Samoa and all airports in Samoa were closed and there were frequent power outages in the area.

Cyclone Heta, the first tropical cyclone of the season and the first to hit Samoa in more than a decade, is expected to continue travelling southeast and would be close to the islands of northern Tonga and Niue by late Tuesday.

TERRA.WIRE