Some residential properties are among hundreds of sites across Sydney potentially contaminated with asbestos-tainted mulch as an expert group is formed to deal with the mounting problem.
Mulch laden with asbestos has already been detected in at least 22 sites after contaminated material was first found at the Rozelle Parklands in Sydney's inner west in January.
"I'm sorry to say but the truth of the matter is that the number of (contaminated) properties would be very large right across Sydney," Premier Chris Minns told reporters on Thursday.
Asked if the likely figure for the number of contaminated sites was in the hundreds, Mr Minns said: "Yes."
That was the "worst case scenario" the state's environmental regulator was working under, it said, while noting nine out of every 10 sites testing so far had been cleared.
The growing scale of the issue and demands on the Environment Protection Authority (EPA) caused an asbestos task force to be assembled on Thursday taking in hazardous material experts and government agencies.
Contact-tracers working to find potential sites containing the contaminated mulch have also had numbers boosted in a bid to speed up the process and reduce exposure to the public.
The workforce now exceeds 130 people.
"Suffice to say it is a very major investigation, probably the largest in the EPA's history," the authority's chief executive Tony Chappell told reporters.
"And we're aiming to bring it to a rigorous conclusion as quickly as possible."
One difficulty facing authorities is the supplier linked to all 22 sites distributed its recycled mulch product to 30 companies, some of whom passed it further down the chain.
The EPA recently learnt a handful of regional sites, including in Nowra, and residential properties had received the mulch product.
Environment Minister Penny Sharpe however denied the government had been too slow to respond.
"What we've realised is from the start of that process through to the bottom of the supply chain, that it's bigger than we think," she told reporters.
Mr Minns said resourcing issues prevented the government from closing all potentially affected parks before they were tested.
"Not every projected park is testing positive to asbestos, but to lock every single park or school or hospital up would be beyond our resources right now," he said.
The latest discovery at a primary school in Liverpool has resulted in hundreds of students learning from home before being shifted to another public school nearby while the mulch is removed.
Education Minister Prue Car said the clean-up would take longer than expected because the mulch had been incorrectly placed.
Opposition environment spokeswoman Kellie Sloane has called for a central register of all sites under investigation by the state's environmental watchdog to be made available to the public.
"The public expects more oversight, they need to understand their government has a handle on this and whether their local park is at risk," she told reporters.
All positive results were being reported on the EPA website, the minister said.
The EPA issued a prevention notice to landscaping supply company Greenlife Resource Recovery after the watchdog determined it supplied the mulch used at Rozelle.
Greenlife has been asked to recall its product voluntarily, with the EPA saying laws around compulsory recalls were not designed for this type of situation.
The company says testing shows mulch stockpiled at its facility was free of asbestos contamination and it was confident the material was also clean when delivered to contractors for landscaping.
It is challenging the prevention order.
