Melbourne is riddled with stockpiles of hazardous and flammable chemicals.

WorkSafe Victoria has revealed up to eight warehouses across Campbellfield and Epping are thought to contain 19 million litres of toxic waste, much more than previously believed.

“It became clear there was significantly more waste material there than we first estimated,” WorkSafe spokesman Michael Coffey said.

The new estimates of the quantity of chemicals is based on engineering drawings of the sites.

“It was extremely difficult to estimate what the volume of the waste was in these warehouses because they were floor-to-ceiling, wall-to-wall stacked with containers and the atmosphere inside was not safe,” Mr Coffey said.

A clean-up operation has managed to remove about 800,000 litres of the waste in the last six weeks.

“We know the substances inside are highly-flammable. We know there's solvents, there's paints, there's oxides, there's basically industrial waste,” Mr Coffey said.

He said investigations into the stockpiles continue.

“What we're seeing at the moment is highly-organised operations that are actively trying to avoid ... regulations.”

Premier Daniel Andrews said it is a challenging situation.

“WorkSafe is doing exactly what it should be doing - checking and then making sure there's corrective action,” he told reporters.

“Our first thing is get the clean-up done. Then second to that, there's about fines and penalties and how you recoup cost of that.”