This satellite image shows Tropical Storm Arthur moving north off the east coast of Florida. Picture: National Oceanic and Atmospheric Administration (NOAA)

Washington - Tropical Storm Arthur became the first hurricane of the 2014 Atlantic season on Thursday after sparking evacuations, closing beaches and tourist sites and disrupting Independence Day celebrations along parts of the US East Coast.

Arthur was about 305km south-southwest of Cape Fear, North Carolina with maximum sustained winds of 75 mph (120kph), the US National Hurricane Centre (NHC) said after upgrading its status.

It was moving at 9 miles per hour (15kph) in a northerly direction toward the coast and is expected to turn toward the north-east with an increase in speed on Thursday.

Authorities had on Wednesday begun closing campgrounds, lighthouses and beaches on the Outer Banks of North Carolina. Several towns and villages rescheduled Independence Day festivities and fireworks plans as the storm picked up speed.

North Carolina Governor Pat McCrory declared a state of emergency on Wednesday for 25 eastern counties to help prepare for possible damage.

Local businesses were worried about losses, though computer forecast models showed the hurricane was not a threat to key oil and gas producing areas in the Gulf of Mexico.

Arthur could be packing Category 1 hurricane-force winds of 85 mph (135kph) when the outer bands brush the Carolinas on Thursday and Friday before weakening, forecasters said.

The storm could also cause dangerous rip currents, rainfall, fierce winds, and flooding along coastal areas of Southern states.

Farther up the coast, the resort town of Ocean City, Maryland, said it was moving its July 4 fireworks display to Saturday because of the storm.

Boston officials also delayed a nationally televised concert by the Boston Pops and a fireworks display, which draw hundreds of thousands of spectators to the city's riverfront.

A tropical storm becomes a hurricane when maximum sustained winds reach 74 mph (119kph). - Reuters