A SpaceX Falcon 9 rocket exploded minutes after liftoff from Cape Canaveral, Florida, following what was meant to be a routine cargo mission to the International Space Station.
"The vehicle has broken up," said NASA commentator George Diller, after NASA television broadcast images of the white rocket falling to pieces.
"We appear to have had a launch vehicle failure," Diller said.
"At this point it is not clear to the launch team exactly what happened."
The California-based company's live webcast of the launch went silent about three minutes into the flight when the rocket could be seen exploding and small pieces tumbling back toward Earth.
Moments later, a SpaceX commentator said the video link from the vehicle had been lost.
"There was some kind of anomaly during first stage flight," he said, noting that the rocket had ignited its nine Merlin engines and reached supersonic speed.
"However it appears something did occur during first stage operations," he added, referring to the stage of rocket flight before the cargo ship would have been able to separate from the first stage of the rocket and reach orbit.