Sacramento, California - Three people were in critical condition after a medical helicopter crashed onto a California highway on Monday, with local authorities saying emergency crews had closed some traffic lanes.

The helicopter crashed just after 7:00 PM PT on eastbound Highway 50 in Sacramento, with flight-tracking data showing it had lifted off from UC Davis Medical Center just minutes before.

A pilot, nurse, and paramedic were on board and taken to hospital after the crash in critical condition, the Sacramento Fire Department said, per CNN.

No patient was on board the helicopter and no road vehicles were involved in the crash, officials said.

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Footage posted on social media showed the helicopter hovering above a row of cars before crashing next to the median in a cloud of smoke.

Bystanders helped first responders lift the helicopter to reach one person trapped underneath, fire officials were quoted as saying.

The South Sacramento California Highway Patrol Area office said the US-50 eastbound and two ramps onto that highway were "shut down with an unknown ETA to reopen."

"Please use alternate routes and expect delays. Additional closures and congestions possible in the area," the office wrote on X Monday night.

The cause of the crash is still being investigated, with the Sacramento County Sheriff's Office saying that it is assisting the highway patrol, CBS News reported.

Sacramento councilmember Lisa Kaplan posted photos showing long lines of traffic on the highway, adding that the freeway was "blocked."

FAA records showed that the helicopter was registered to REACH Air Medical Services, CNN reported.

Kirsten Gurmendi, public relations director at REACH's parent Global Medical Response, said the company was aware of the accident and that no patient was on board.

"We are in the process of determining the details of this situation, as well as the condition of the REACH crew involved, who were all taken to area hospitals," Gurmendi told AFP.