The clean-up is continuing after a fuel spill at a refinery in Melbourne's west.

An eight million litre tank began leaking unleaded petrol at the Mobil refinery in Altona, just before midnight.

The tank held 3.5 million litres of fuel and 16,000 litres leaked from the tank.

More than 50 fire fighters poured foam on the spill to stop the fumes from igniting, and the remaining fuel has been drained from the tank.

Bruce Dawson from the Environment Protection Agency (EPA) says there is no risk to the public, or the surrounding wetlands.

"The petrol that has leaked has been contained within a bund," he said.

The Victorian Greens MP, Colleen Hartland, says the spill should not have happened at all.

She says the tanks at the Altona refinery are old, and poorly maintained.

"Every two years we have an accident like this," she said.

"Every few years the Government says it won't happen again and it happens again."

"So as a resident, you really start to lose faith in the prevention strategy," she said.

Glen Henson, from Mobil has rejected the claims.

"We've done a lot of work on tank maintenance and our objective is to get to these issues ahead of time," he said.

The EPA will investigate what caused the spill.