The Environment Protection Authority (EPA) on Thursday said suspected asbestos was found at five more parks in Melbourne's southwest: three at Altona Meadows, one at Altona and one at Newport.

The authority was waiting on lab testing to corroborate its fears after asbestos was confirmed at eight other sites.

Several other parks have been cleared of contamination.

Hobsons Bay City Council, wherein six sites have been confirmed as contaminated, has been a key focus of inspectors' investigation over the source of asbestos.

Altona Coastal Park is the latest in the area to test positive, while contamination at Fitzgerald Square Reserve at Sunshine West in Melbourne's west was also confirmed.

The authority said it inspected two of the council's key mulch producers and did not find asbestos in the mulch for sale.

Some of the mulch inspectors have been looking through was laid before 2015, two years before the regulation of commercial mulch producers in Victoria.

"While investigations continue, it appears that the two most likely sources of asbestos contamination are deposits after mulch is laid or it was already on the site and mulch laid over it, including new mulch that has been deposited on top of older mulch still present at the site," the regulator said on Wednesday.

"Hobsons Bay City Council has now inspected 15 out of 21 parks it has currently identified where mulch has been laid in the last 18 months."

Hobsons Bay council voted to urged the state government to emulate NSW by setting up an asbestos task force.

But the EPA has rubbished the idea, insisting it does not need more help.

"We don't need any more resources to address it," the authority's Duncan Pendrigh told ABC radio on Thursday.

The NSW asbestos task force was announced in February to support the state's environment watchdog after asbestos was found in mulch at Sydney's Rozelle Parklands.

Seventy-five sites across the city tested positive for asbestos.

All pieces of the cancer-causing material found in Melbourne are bonded in cement and non-friable, meaning they pose a lower risk.

The authority has homed in on demolition companies as the potential source of asbestos contamination.

Premier Jacinta Allan said the authority had more tools and powers to investigate than NSW's regulator.

"We have a very different regime that is in place here in Victoria," she told reporters.

Opposition environment spokesman James Newbury said the problem was much larger than the authority initially suggested and demanded a broad audit of state land.

"Asbestos is dangerous and every day we learn of newly confirmed sites where it is in parks near children," he said.

Separately, the authority has confirmed a magistrate fined the owner of a demolition company $25,000 for leaving 150kg of asbestos-containing industrial waste exposed on a Spotswood site in 2021.

STATUS OF POTENTIAL MELBOURNE ASBESTOS SITES:

Hobsons Bay City Council:

Truganina Park, Altona Meadows - awaiting test results

Doug Grant Reserve, Altona - awaiting test results

HD Graham Reserve, Altona Meadows - awaiting test results

Laverton Creek at the rear of AB Shaw Reserve, Altona Meadows - awaiting test results

Newport Lakes Reserve, Newport - awaiting test results

Altona Coastal Park, Altona - confirmed

PA Burns Reserve, Altona - confirmed

GJ Hosken Reserve, Altona North - confirmed

Crofts Reserve, Altona North - confirmed

Dennis Reserve, Williamstown - tested negative

PJ Lynch Reserve, Altona North - confirmed

Donald McLean Reserve, Spotswood - confirmed

Brimbank Council:

Fitzgerald Square Reserve, Sunshine West - confirmed

Merri-bek City Council:

Shore Reserve, Pascoe Vale South - confirmed

Australian Associated Press