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 believed the aircraft is a medical helicopter.

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

It is understood there was a nurse, paramedic and pilot on board the flight.

The crash left one person trapped under the helicopter, CNN reports.

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

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

More to come.

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