A woman speaks into a cellphone asking for help at her flooded residence in Lumberton, North Carolina, the United States, on Sept. 15, 2018 in the wake of Hurricane Florence. (AFP Photo)

WASHINGTON, Sept. 16 (Xinhua) -- At least 15 people have been killed in North Carolina and South Carolina in the United States as a result of Hurricane Florence which is downgraded to a tropical storm.

The weakened Florence is still battering the region with heavy rain on Sunday, causing "catastrophic" flooding and leaving more than one million homes without power.

More than 900 people have been rescued from the rising floodwaters by local authorities, volunteers and the U.S. Coast Guard since Friday morning.

The storm surge of up to 13 feet (3.9 m) will be "life threatening" and rainfall of up to 40 inches (101.6 cm) will mean "catastrophic" flooding, according to the National Hurricane Center.

According to the U.S. National Weather Service, there are 5.25 million residents in areas under hurricane warnings or watches, and 4.9 million in places under tropical storm warnings or watches.