Late yesterday the cyclone moved offshore from Samoa after causing major damage in the capital Apia, with buildings destroyed and flooding across the city.
A state of disaster has been declared in the Pacific nation.
Ministry of Natural Resources and Environment's Taulealea Usunai said the cyclone may change its course back towards Samoa.
"There is a possibility that it may turn around," Mr Usunai said.
"At the moment we are coping. But in calling for international assistance during the cyclone, it will be difficult to get help into the country because airports are closed and so are the ports."
The US territory American Samoa was also preparing to be hit by Cyclone Evan, but so far has only been affected by high winds with no reports of damage overnight.
The storm is currently near the tip of Samoa's Upolu island.
A gale force wind warning remains in force.
The category-two storm made landfall in Apia on Thursday, bringing heavy rainfall and winds of up to 110 kilometres per hour.
Thought to be one of the most powerful to hit the Pacific nation in 20 years, the cyclone also forced the closure of the airport.
On Thursday local reporter Cherelle Jackson said trees had been torn down and there was flash flooding across Apia.
"There has been flash flooding all over town, blocking the roads, and people have been kept from their homes," Ms Jackson told Pacific Beat, adding that emergency services were working to clear the roads.
"Just where I am two of our neighbours have evacuated. Their houses have been flattened.
"Power poles are down, breadfruit trees, taro trees, banana trees - the staple of part of our diet, they're just all over the road."
Monica Miller, Radio Australia's reporter in Pago Pago, said people were boarding up their homes and schools were closed.
"Some of the people started making preparations yesterday, while others started this morning," she said.
"There are designated shelters, usually church halls, that people can go to if they are inundated."
Evan is the first named cyclone of the South Pacific's summer cyclone season.
The UN Disaster Management Office in Samoa and the country's disaster advisory committee have met to discuss the potential impact and necessary preparedness measures.