WATCH: Passenger plane loses turbine casing while flying to Hawaii

Passengers onboard a flight headed for Hawaii have been left horrified after the casing around one of the plane's turbines flew off mid-flight.

United Airlines flight UA1175 was travelling to Honolulu from San Francisco on Tuesday local time when one of the plane's engines was stripped bare of its paneling.

Passenger Erik Haddad said the terrifying ordeal began 36 minutes before the plane was due to land on the Pacific island.

A 7700 distress call was submitted by the plane's crew which meant all air traffic control facilities in the area were aware of the plane's emergency situation.

Haddad, alongside other passengers, took to Twitter to share remarkable footage and images of the bare turbine shaking in the wind.

"The scariest flight of my life," passenger Maria Falaschi wrote online.

Despite the onboard panic, Mr Haddad managed to keep his cool, tweeting an image of the damage alongside the safety manual captioned: "I don't see anything about this in the manual."

The plane managed to land safely in Honolulu 22 minutes late at 1.02pm (10.02am AEDT) while Aircraft Rescue and Firefighting arrived to inspect the cause of the incident.