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 form a 30,000L 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.
Captain Andrew Hayton, harbourmaster at Waitemata Harbour, said there was no danger of the diesel getting into the sea.