A United Airlines plane on a flight from Los Angeles to Sydney has landed at Sydney Airport after the pilot issued a mayday alert.

The plane was low on fuel and made the mayday call shortly after 6am on Thursday as a precaution.

The Boeing 787, carrying 180 passengers and 14 crew, landed without incident about 6.30am and no passengers were at risk, an Airservices Australia spokeswoman said.

The mayday call prompted a full emergency response at the airport.