A United States Air Force B-52 Stratofortress has crashed shortly after taking off from Edwards Air Force Base in the state of California, with eight people feared to have died.

"An Air Force B-52 Stratofortress carrying eight people on a routine test mission crashed today shortly after take-off at 11.20 am (PDT). Initial indications are that the crash was not survivable," said a statement issued by Edwards Air Force Base.

Emergency response personnel are on the scene, and officials are working to account for all personnel.

The aircraft went down in Kern County, California, according to officials.

Earlier, the base announced the closure of the airfield, with all inbound aircraft diverted.

"All non-commercial visitor passes have been suspended until further notice to allow the installation to focus entirely on emergency response operations," it added.

Pentagon blocks further details

Edwards Air Force Base, California, and Air Force Pentagon headquarters referred questions to the initial announcement of the crash and declined to provide additional details.

"More information will be provided as it becomes available," the base added.

The B-52 typically operates with a crew of five, including two pilots, a radar navigator, navigator and electronic warfare officer, though eight personnel were on board for this specific flight.

The aircraft is one of 76 B-52s remaining in the Air Force inventory.

The fleet is expected to remain in service for decades as the Air Force pursues extensive modernisation upgrades.

The nuclear-capable bomber first entered service in the 1950s and remains a central component of the US strategic bomber force.