Three people critically injured after helicopter crashes onto busy California highway

Three people have been critically injured after a helicopter crashed onto a major highway in California, USA.

Authorities responded to a helicopter crash on Highway 50 in Sacramento earlier today (Monday night local time).

It is understood the aircraft is a medical helicopter.

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FAA records show the helicopter was registered to REACH Air Medical Services.

Sacramento's fire department reported three people were left in critical conditions.

Sacramento Fire Captain Justin Sylvia told reporters the injured are a nurse, paramedic and a pilot.

"The captain immediately sequestered the help of just civilians that were standing around. They were able to lift part of that helicopter out and get that victim out," Sylvia said.

"There's a pretty large debris field," Sylvia said, saying it was "extremely lucky" that there weren't more victims.

The crash left one person trapped under the helicopter.

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Bystanders reportedly rushed to help lift the aircraft off the trapped victim.

Sacramento Mayor Kevin McCarty described the crash as "harrowing" and praised witnesses for their rescue efforts.

"There has been a harrowing helicopter crash on 50 eastbound west of 59th St. Thank you to our brave first responders and ~15 bystanders who assisted Sac Fire until more units arrived on scene," McCarty said.

"Survivors are being treated at local hospitals."

Vision from the scene shows the helicopter wreckage in the middle of the road as traffic banked up behind it.

The helicopter had taken off from the University of California Davis Medical Centre in Sacramento and was heading north before the crash, according to flight tracking website Flightradar24.

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