Flight UA2477 originated in Memphis, Tennessee.
The Boeing 737 Max 8 plane appeared to suffer the gear failure during the last 30 minutes of the flight, according to reports.
All passengers have been evacuated safely from the aircraft, but it is not clear what happened in the incident.
Details on possible injuries have not yet been reported.
At the time, weather conditions consisted of heavy rain and reduced visibility. Photos show the plane stuck in a ditch with its nose in the air.
Friday's incident comes one day after a United Airlines jetliner bound for Japan made a safe landing in Los Angeles. It lost a tire while taking off from San Francisco.
Videos show the plane losing one of its six tires on its left-side main landing gear assembly seconds after takeoff. The tire landed in an employee parking lot at San Francisco International Airport and smashed into a car, shattering its back window.
No one was injured in the incident, according to an airport spokesperson.
Comment: Footage of both incidents:
The Boeing 777 made an uneventful landing at LAX and stopped about two-thirds of the way down a runway.
The flight, which carried 235 passengers and a crew of 14, was built in 2002 and was designed to land safely with missing or damaged tires, the airline said.
The passengers were moved to another plane for the rest of the trip, United said.
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