A tropical depression is gaining intensity as it moves towards Samoa, and is likely to develop into a cyclone within the next 12 to 24 hours.
The country's Meteorological Service says the system is about 550km northwest of Savai'i and 650km northwest of the capital, Apia.
It is expected to move east-southeast at nine knots and slowly intensify into a tropical cyclone overnight as it nears the country.
A spokesperson, Luteru Tauvale, said the country was already experiencing strong winds and heavy rains, and people should be prepared for it to get worse.
"The general advice is for people to take extra care of the strong winds, also in terms of the heavy rain it may cause floods."
Small craft and fishing boats should also avoid going out into very rough seas, he said.
Storm watch for American Samoa
The US National Weather Service has issued a tropical storm watch for neighbouring American Samoa.
While the system isn't expected to pass close to American Samoa - to Samoa's east - the territory is being warned to prepare for strong winds and heavy rain, which could cause flooding and landslides.