United Airlines could not be immediately reached for a comment.
Police called a "full emergency response" and briefly closed major roads surrounding Sydney airport as a precaution at 6:36 am (2036 GMT Wednesday) after the pilot raised the alert.
"There's an global standard that requires that once you get down to your fuel reserve in a flight that you have to declare what is called a 'fuel mayday, '" Gibson said.
The Sydney Morning Herald reported that 180 passengers and 14 crew disembarked safely.
A United Airlines plane landed safely at Sydney Airport Thursday after low fuel reserves triggered a mayday call from the pilot.
"There's an global standard that requires that, once you get down to your fuel reserve in a flight, you have to declare what is called a "fuel mayday", Mr Gibson said.
NSW Police confirmed a full emergency response was launched when the mayday call was made.
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United Airlines called it a mechanical issue and said all on board were safe.
Gibson said stronger headwinds than were forecast for the 12,000-kilometer (7,500-mile) flight across the Pacific could burn more fuel than planned.
Passengers who were on-board the plane told 9NEWS they were not made aware of the incident as the plane came in to land.
Indeed, according to the BBC, the plane would have had enough fuel to last at least 45 minutes.
"No passengers were at risk at any time", a spokeswoman for Air Services Australia told Reuters.
"Not a hint, not a mention of any impending doom or mayday situation", she said.
An Airservices Australia spokesperson said instances like this were "not unusual".