Eight crew believed dead in California B-52 bomber crash

Eight people aboard a B-52 bomber that crashed at a US Air Force base in California are believed to be dead.

"Initial indications are that the crash was not survivable," the Edwards Air Force Base posted on social media.

There was no information on the crew, however, aerial footage showed virtually nothing left of the aircraft.

Black smoke rose from a large swathe of charred desert at Edwards Air Force Base near what appeared to be a runway, with emergency vehicles nearby.

The military did not say whether the bomber was armed, with investigations ongoing.

Bomber used to carry nuclear weapons

The Boeing B-52 Stratofortress is a long-range bomber that entered service in 1955.

The bomber is designed to carry conventional and nuclear weapons, and it has been used in conflicts involving the US military from Vietnam to Iran.

In a conventional conflict, the B-52 can perform strategic attack, close-air support, air interdiction, offensive counter-air and maritime operations, according to a US Air Force fact sheet.

The airfield remains closed, and all inbound aircraft are being diverted.

Non-commercial visitor passes for the base were suspended "to allow the installation to focus entirely on emergency response operations", officials said in a statement.

Edwards Air Force Base is home to a large portion of the US Air Force's aircraft test and development efforts and is about 161 kilometres north of Los Angeles.

The 412th Test Wing, which runs the base, also conducts developmental testing of all Air Force aircraft, weapons systems, software and components before purchase by the service as well as throughout their life span.

The vast desert base is also where Air Force test pilot Chuck Yeager reached a speed of Mach 1.05 to break the sound barrier for the first confirmed time in 1947.

Expert suspects flight control malfunction

The way the B-52 crashed so quickly after take-off without getting very high makes aviation safety expert Jeff Guzzetti suspect some kind of flight control malfunction.

It is possible the controls were rigged incorrectly after maintenance, or there was a catastrophic engine problem or a failure of a piece of equipment being tested, he said.

"I think it was definitely a controllability issue. Now, whether that was tied to an engine failure, a flight control failure, or some new testing device failure, I'm not sure," Mr Guzzetti said.

Although the Air Force has been flying B-52 bombers for more than 70 years, testing new equipment on a plane can create new challenges.

"A flight test is always riskier than normal operations, so that's why you have specially trained test pilots, and you should have other safety protocols," Mr Guzzetti said.

AP/ABC