Florence, a Category 1 hurricane, continues to strengthen as it's approaching the U.S. East Coast, and is expected to become a major hurricane by Monday night, the U.S. National Hurricane Center (NHC) said Sunday.

The center of the hurricane was located about 905 km northeast of the northern Leeward Islands, packing maximum sustained winds of 150 km per hour (kph), moving west at 11 kph, according to the latest advisory published by the weather forecaster.

"Florence is forecast to rapidly strengthen to a major hurricane by Monday night, and is expected to remain an extremely dangerous major hurricane through Thursday," the advisory added.

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.

Hurricanes reaching Category 3 and higher are considered major hurricanes because of their potential in causing a significant loss of life and damage.

Florence, the first major hurricane of the Atlantic season, was once a Category 4 hurricane last week, packing maximum sustained winds of 215 kph, before weakening gradually to a tropical storm, which regained hurricane strength Sunday morning

Besides Florence, the Atlantic Ocean's sixth named storm of 2018, two other storms, Isaac and Helene, are churning in the Atlantic basin.