Alarming footage shows the moment a Boeing 787's nose gear collapses while the Lufthansa plane is parked at its gate ... and the incident caused several injuries.

The travel nightmare went down Thursday at Frankfurt Airport in Germany ... crew members and ground staff were on ​board the jetliner when the "nose landing gear unexpectedly retracted" ... according to the airline.

Lufthansa says several employees were injured and are receiving medical treatment, adding ... "We are currently investigating the exact circumstances in cooperation with the relevant authorities."

You can see in the video ... the plane is parked at the gate when the nose gear gives out and the front of the plane falls to the tarmac. It's unclear if the collapse was caused by faulty equipment or human error.

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According to FlightRadar24, the plane -- which reportedly was only built last year and entered into service in February -- was set to take off for Los Angeles.

Lufthansa says the mishap occurred before passengers were set to board.

Needless to say, the flight was canceled.