Hurricane Joaquin has strengthened into a Category 3 storm as it nears the Bahamas, the National Hurricane Center (NHC) says.

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 Bahamas that could see winds of up to 115mph.

The NHC says hurricane Joaquin, the third of the Atlantic season, could affect the US East Coast by October 4.

Photo ABC News

It warned that Joaquin “could become a major hurricane” by October 2. It picked up considerable strength on September 29, 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 Joaquin’s path, such as San Salvador, Rum Cay and Cat Island, which all have small populations.

Officials in New York, New Jersey and Connecticut, states badly affected by Superstorm Sandy in 2012, warned residents should begin making preparations.

Virginia’s Governor, Terry McAuliffe, has declared a state of emergency in response to heavy flooding earlier in the week, and because of what he called “a serious threat to life and property” from Joaquin.

A White House spokesman said the Federal Emergency Management Agency (FEMA) was following the progress of Joaquin and preparing in case it made landfall in the US.