An unmanned commercial supply rocket bound for the International Space Station exploded moments after liftoff, with debris falling in flames over the launch site in eastern Virginia.

No injuries were reported following the first catastrophic launch in Nasa's commercial spaceflight effort.

The accident at Orbital Sciences Corporation's launch complex at Wallops Island was sure to draw criticism over the space agency's growing reliance on private US companies in this post-shuttle effort.

Nasa is paying billions of dollars to Orbital Sciences and the SpaceX company to make station deliveries, and it is counting on SpaceX and Boeing to start flying US astronauts to the orbiting lab as early as 2017.

Nasa spokesman Rob Navias said there was nothing on the lost flight that was urgently needed by the six people living on the space station.

Orbital Sciences' Antares rocket blew up over the launch complex, just six seconds after liftoff. The company said everyone at the site had been accounted for, and the damage appeared to be limited to the facilities.

Flames could be seen shooting into the sky as the sun set. There was no hint of any trouble until the rocket exploded. This was the second launch attempt for the mission.

Monday evening's try was thwarted by a stray yacht in the rocket's danger zone. The restrictions are in case of just such an accident that occurred yesterday evening.

"We will understand what happened - hopefully soon - and we'll get things back on track," Orbital Sciences' executive vice president Frank Culbertson told his team an hour after the failure.

"We've all seen this happen in our business before, and we've all seen the teams recover from this, and we will do the same."

The roomful of engineers and technicians were ordered to maintain all computer data for the ensuing investigation. Mr Culbertson advised his staff not to talk to news reporters and to refrain from speculating among themselves.

"Definitely do not talk outside of our family," said Mr Culbertson, a former astronaut who once served on the space station.

It was the fourth Cygnus bound for the orbiting lab. The first flew just over a year ago.

The Cygnus cargo ship was loaded with 5,000lbs of experiments and equipment and the Russian Space Agency was proceeding with its own supply run today.

But the scientists and students behind all the science research on board were surely devastated. About one-third of the contents of the Cygnus involved science research.

Among the instruments that were lost were a meteor tracker and 32 mini research satellites, along with numerous experiments compiled by schoolchildren.

The two Americans, three Russians and one German on the orbiting lab were informed promptly of the accident.

Until yesterday, all of the supply missions by the Virginia-based Orbital Sciences and California-based SpaceX had been near-flawless.

President Barack Obama has long championed this commercial effort, urging that Nasa focus its human spaceflight effort less on nearby orbit and more on destinations like asteroids and Mars.

Sign up to our free newsletters

Get the best updates straight to your inbox:
Please select at least one mailing list.

You can unsubscribe at any time by clicking the link in the footer of our emails. We use Mailchimp as our marketing platform. By subscribing, you acknowledge that your information will be transferred to Mailchimp for processing.