Hurricane Joaquin has strengthened into a Category 3 storm, warn forecasters, as it nears the Bahamas.

The US National Hurricane Centre confirmed the eye of the storm is expected to pass over eastern islands of the Bahamas overnight.

A hurricane warning is in effect for much of the country, with residents warned to expect winds of up to 115 mph.

The NHC warned Joaquin “could become a major hurricane” by Friday as it approaches the east of the United States. It picked up considerable strength on Wednesday, after being upgraded from a storm to a category 3 hurricane, on a scale of five, in only a few hours.

Geoffrey Greene, a senior forecaster with the Bahamas Meteorology Department, said he was “very concerned” about some of the smaller islands in the path of the storm.

The populations of San Salvador, Rum Cay and Cat Island are thought to be at particular risk.