The plane was headed to Honolulu after taking off from San Francisco International Airport just after 9 a.m. and landed safely at 2:42 p.m. Pacific time after the pilots called for an emergency landing.
The damaged engine is seen in video a passenger tweeted from United Flight Airlines Flight 1175.
The aircraft involved is a Boeing 777. It has two engines and is designed to fly on just one engine for more than three hours over water.
United Airlines released a statement about the incident:
"Our pilots followed all necessary protocols to safely land the aircraft. The aircraft taxied to the gate and passengers deplaned normally. United is fully cooperating with the NTSB and FAA investigation of the event. We are currently reaching out to all of our customers on this flight, and plan to fully refund every ticket."