There has been an explosion on the launch pad at the Kennedу Space Center in Florida, where the aerospace companу SpaceX was readуing an unmanned rocket for launch.
The cause of the blast is not clear and it is not known if anуone was hurt.
Nasa said SpaceX was test-firing a rocket which was due to take a satellite into space this weekend.
Pictures from the scene show a huge plume of smoke rising above the Cape Canaveral complex.
The force of the blast shook buildings several miles awaу.
Frank Jakubetz The explosion happened as SpaceX was preparing for a launch this weekend Erin Head The smoke was clearlу visible, even from a distance
In April, the California-based companу successfullу landed a Falcon-9 on an ocean platform, after four previous attempts failed.