WASHINGTON, Sept. 9 (Xinhua) -- Tropical Storm Florence has turned into a hurricane and is expected to rapidly intensifying into a major hurricane by Monday, the U.S. National Hurricane Center (NHC) said Sunday.

The center of the hurricane is located about 1,210 kilometers southeast of Bermuda, with maximum sustained winds of 121 kilometers per hour (kph), moving west at 9 kph, the hurricane center said.

On the forecast track, the center of Florence will travel between Bermuda and the Bahamas on Tuesday and Wednesday before approaching the southeastern U.S. coast on Thursday.

The Miami-based center said Florence is forecast to rapidly strengthen to a major hurricane by Monday, and is expected to remain an extremely dangerous major hurricane through Thursday.

A Category 4 storm packs winds of 209 kph or more and has the potential for catastrophic damage.

The governors of North and South Carolina and Virginia declared states of emergency to give them time to prepare. The U.S. Navy said ships in Virginia's Hampton Roads area would leave port for their own safety.

Dangerous swells generated by Florence affected Bermuda and have begun to reach parts of the U.S. East Coast, added the NHC.

Florence, the first major hurricane of the Atlantic season, was once a Category 4 hurricane last week, packing maximum sustained winds of 215 km per hour.

Besides Florence, the Atlantic Ocean' s sixth named storm of the year, two other storms, Isaac and Helene, are churning in the basin.