The fuel pipeline from Marsden Point to Auckland has been shut down following an alarm from the leak detection system.
The alarm has gone off in a section of the line between Wiri and Marsden Point.
All fuel types are affected but aircraft refuelling operations at Auckland Airport are continuing as normal.
Refining NZ spokesman Greg McNeill said the refinery was closed at 5.15am this morning as a precautionary measure after the monitoring system alarmed.
"Refinery staff are currently carrying out checks to determine the pipeline is fit for service.
"The situation is different to that in September and at this moment, pending our investigation, we are hoping to be able to return to normal service later in the day," he said.
A BP spokeswoman said it was liaising with Refining NZ to understand when the pipeline will return to normal operation.
"Each fuel company is individually working to put alternative supply arrangements in place to minimise impacts on customers.''
A Flight Centre spokeswoman said it is too early to tell if there will be any impacts on travel plans.
Earlier this year, the fuel pipeline burst near Ruakaka, spilling up to 80,000 litres of fuel on nearby farmland and causing severe disruption to flights.
The travel plans of thousands of people were affected during the crisis, which saw the cancellation of scores of flights in September.
The HMNZS Endeavour was eventually deployed to transport fuel and 20 Defence Force category 5 tanker drivers hit the roads between Marsden Point and the airport.
An Auckland Airport spokeswoman said, "All we have been told is the pipeline has been shut down while they investigate an alarm that went off.
"From our perspective at the moment, it is exactly that, and we are operating as usual until we are told further."
She said fuel is supplied directly to the airlines, and not to the airport itself.
"The pipeline supplies the Wiri storage facility, and that is the pipeline that is closed at the moment.
"The oil companies keep jet fuel in storage there, and also at a storage facility at the airport called Juhi. Out of there they refuel their trucks and supply fuel directly to the airline."
She said the airport itself is not responsible for flight cancellations, but that lies in the hands of the airlines.
"The fuel companies work out their fuel allocations with their customers, which are the airlines, and then the airline makes a decision on what they operate and what they can't."