Up to 30,000 litres of diesel has leaked from a tank at the Devonport Naval Base.
A fire service spokesman said the fuel was leaking from a 30,000-litre tank at the base.
"It appears to not have entered into any waterways or into the sea at this time," he said.
Emergency services were called to the scene at 12.30pm.
The New Zealand Defence Force is yet to comment on the incident.
An Auckland Council spokeswoman said the council was investigating the incident.
Captain Andrew Hayton, harbourmaster at Waitemata Harbour, said there was no danger of the diesel getting into the sea.
It is understood that Auckland Council's pollution response team is at the naval base.
