During a regional media briefing on Monday, NSW Deputy Premier John Barilaro said sewage surveillance results will be one of the factors used to decide which local government areas (LGAs) - if any - will come out of lockdown when it finishes this Friday.

"What we will be looking at is how many active cases there are in a region and how many of them were actually in the community and infectious," he said.

"If people have been in isolation and they've been in isolation for their period, that'll be discounted.

"We'll be looking at which LGAs are in close proximity to other LGAs that have got high numbers, so LGAs around Dubbo will be an area of concern. We'll be definitely looking at LGAs with sewage surveillance detection as well."

A crisis meeting will make a decision on regional NSW lockdown on Wednesday afternoon, which will be announced on Thursday.

Tamworth recorded its fourth mystery positive sewage test for COVID-19 in a row on Saturday, with additional test results due on Wednesday.

With no known cases in the community, the source of the detection is unknown.

Mr Barilaro has also indicated that some regions which stay in lockdown beyond September 10 will remain under stay-at-home orders until the state reaches its first 70 per cent adult vaccination target.

If the current pace of vaccination rollout continues, the state will reach the 70 per cent target on Monday, October 18, he said.

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"Dubbo, Wilcannia, Broken Hill, the Central Darling and some of the Central West LGAs like Bathurst, Orange which have got consistent cases, the reality is they're never going to get back to zero," he said.

"They will continue to have cases and they will be tied and locked in to what happens in Sydney until the 70 per cent double dose target is reached.

"But there are areas where there might be just one case that's come through like, let's say, Bateman's Bay - one case, hasn't been in the community, goes through the 14 days isolation.

"They might miss out on getting out of lockdown this weekend but you could possibly reconsider that in a couple of weeks - well you should, I think you should give those regions every opportunity to come out."

COVID-19 fragments were also detected in wastewater in Glen Innes on Saturday, and Gunnedah last Wednesday despite no known cases.

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