An unmanned SpaceX rocket exploded about two minutes after lift-off from Florida, destroying a cargo ship bound for the International Space Station in the latest in a string of mishaps in supplying the orbiting outpost.
The 63-metre-high Falcon 9 rocket, built and flown by SpaceX, which is owned by technology entrepreneur Elon Musk, had previously made 18 successful launches since its 2010 debut. Those included six cargo runs for Nasa under a 15-flight contract worth more than €1.8bn.
The accident soon after liftoff from Cape Canaveral Air Force Station was the second successive botched mission to resupply the space station.
A Russian Progress cargo ship failed to reach the outpost in April following a problem with its Soyuz launcher. Russia plans to launch a replacement capsule on Friday.
The cause of the explosion was not yet clear, officials said.
"This was a blow to us. We lost a lot of research equipment on this flight," said Nasa associate administrator Bill Gerstenmaier.
An investigation into the explosion will ground the Falcon 9 rockets for "a number of months or so" but less than a year, SpaceX president Gwynne Shotwell said.
A preliminary analysis indicated a problem with the rocket's upper-stage engine, SpaceX founder Elon Musk said on Twitter.
The ISS has about four months of food and supplies on board, so the accident does not pose an immediate problem.