A rocket that was to resupply the International Space Station blew up Tuesday night a few seconds after lift-off from Wallops Island, Va. (NASA)

An unmanned rocket that was to resupply the International Space Station blew up Tuesday evening a few seconds after liftoff from Wallops Island, Va.

The Orbital Sciences rocket rose a short distance from the launchpad and then exploded in a ball of orange flames. Orbital Sciences is a private company based in Dulles, Va.

NASA confirmed that all personnel were accounted for and that there were no injuries in the explosion. However, it appeared that the explosion caused damage on the ground. Emergency personnel from nearby Virginia jurisdictions, including Chincoteague, were sent to the scene.

The cause of the explosion was not immediately known.

At a news conference Tuesday evening, NASA described the explosion as a “catastrophic anomaly.”

At liftoff, rockets are filled with highly volatile fuel, including kerosene, and flight is considered risky.

Officials reiterated that any specific determination of what went wrong would take time. Witness accounts of what happened varied somewhat. Some said that the rocket appeared to catch fire within seconds after liftoff, then fell back to the launchpad and exploded.

The explosion directed new attention to the commercial space flight program. In contrast to earlier years, the commercial program involves craft that are built and operated by private companies.

Officials indicated Tuesday night that they were determined to continue with the program. An Orbital Sciences official said that when the cause is identified, “we will begin the necessary work to return to flight.”

NASA’s William Gerstenmaier said the failed attempt “will not deter us” from working to expand the “already successful” capability of supplying the space station from the United States.

Shortly after the explosion, CNN quoted a launch director as saying that the spacecraft contained classified “crypto” equipment, but early Wednesday a NASA spokesman said by email that “We didn’t have any classified items on board.”

Orbital Sciences had conducted previous resupply missions from Wallops Island under a contract with NASA. However, Tuesday’s launch was to be the first in which a more powerful second-stage motor was to be used.

The launch was scheduled for 6:22 p.m. from the facility on the Eastern Shore of Virginia. Had all gone according to plan, the launch would have been visible for hundreds of miles along the Eastern Seaboard, and as far west as Pittsburgh.

Many people had gathered in anticipation of the launch, from the Eastern Shore to the Washington area. The White House said President Obama was briefed on the explosion. The crew of the space station reportedly witnessed the accident on a video feed.

Plans called for a two-stage Antares space launch vehicle to boost a Cygnus spacecraft into orbit. The compartment that carried the Antares payload was about 12 feet in diameter, at the top of the long, slender Antares.

After reaching orbit, the spacecraft was then to dock with the space station.

The first stage employed a liquid-fueled­ rocket that was powered by two Aerojet Rocketdyne AJ26 engines, according to Orbital Sciences.

The second stage was to use a solid motor to boost the Cygnus into orbit. Orbital said the mission was the first to use a larger, more powerful Castor 30XL second-stage­ motor.

Orbital Sciences has contracted with the space agency to resupply the space station. The rocket was carrying about 5,000 pounds of food and other cargo.

At the news conference, it was asserted that the value of the rocket and spacecraft was more than $200 million. The financial effect of the loss on the parties involved could not be learned immediately.

Authorities said at the news conference that the space station crew had no urgent needs and could continue operations for some time without the cargo that was to be brought on the Cygnus.

Successful resupply missions have been carried out under the $1.9 billion contract with Orbital Sciences. Tuesday’s launch was to be the third cargo mission to the space station by a Cygnus spacecraft.

The explosion may have been the most spectacular launch failure at the Wallops Island facility, on the edge of the Atlantic Ocean. Video showed a cloud of smoke and a fireball, with small pieces of debris ejected from the center of the explosion.

Previously, the resupply missions to the space station were conducted with NASA’s space shuttles. The space shuttle program ended in 2011. Orbital Sciences and NASA, among others, will investigate the accident.

The cargo in the Cygnus included students’ science experiments.