An unmanned Antares rocket exploded seconds after lift-off from a commercial launch pad in the US state of Virginia.

It was the first accident since NASA turned to private operators to deliver cargo to the International Space Station.

The 14-storey rocket, built and launched by Orbital SciencesCorp, blasted off its seaside launch pad at the Wallops Flight Facility at 6.22pm (10.22pm Irish time) carrying a Cygnus cargo ship for the space station.

It exploded in a huge fireball moments later.

The cause of the accident was not immediately known, said NASA mission commentator Dan Huot.

Mr Huot said there were no reports of any personnel in the vicinity of the explosion.

Orbital Sciences said in a statement: "We've confirmed that all personnel have been accounted for. We have no injuries in the operation today."

NASA launch control said damage appeared to be limited to the launch facility and rocket.

The Antares rocket had been launched successfully on four previous missions.

"This has been a lot of hard work to get to this point," Orbital Sciences Executive Vice President Frank Culbertson told the launch team just before lift-off.

The launch had been delayed one day after a boat sailed into a restricted safety zone beneath the rocket's intended flight path.

NASA tweeted after the explosion to confirm that no injuries were reported.

Virginia-based Orbital Sciences is one of two companies hired by NASA to fly cargo to the station after the space shuttles were retired.

The planned flight was to be the third of eight under the company's $1.9bn (€1.5bn) contract with NASA.

The second US supply line to the station is run by privately owned Space Exploration Technologies, or SpaceX, which is preparing for its fourth flight under a separate NASA contract.

Outfitted with a new, more powerful upper-stage engine, the Antares rocket carried a Cygnus spacecraft packed with 2,293 kg of supplies, science experiments and equipment - a 15% increase over previous missions.

Cygnus was to loiter in orbit until 2 November, then fly itself to the station so astronauts could use a robotic crane to snare the capsule and attach it to a berthing port.

The station, a research laboratory owned and operated by 15 nations, flies about 418km above Earth.

In addition to food, supplies and equipment, the Cygnus spacecraft was loaded with more than 725kg of science experiments, including an investigation to chemically analyse meteors as they burn up in Earth's atmosphere.