Fragments of the virus have been detected in Dubbo's sewage from a sample taken on Tuesday, prompting strong words from the western region health chief.

"One thing we absolutely know is there has been people with COVID-19 in our region over the last week or 10 days," Western NSW Local Health District chief executive Scott McLachlan told media on Thursday.

"This is time for us to be absolutely vigilant, not for a second should we be relaxing or thinking that Western NSW is free from COVID."

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There were no new active cases reported for the region in the past 24 hours, and no known cases in Dubbo. The next two days are crucial, and it's important for people to get tested.

"There's some real urgency around people coming to get tested if you've got any signs or symptoms, or concerns, however mild," Mr McLachlan said.

"We'll be increasing the capacity of the showground testing site...we really do want to see anyone from Dubbo or the surrounding communities come out to get tested."

The fragments may be from shedding of the virus by someone who has previously had it, but is no longer infectious, or it could be from someone who visited the region but is no longer here.

If an active case is detected in Dubbo, there's a strong chance the region will be put into an Orange-style lockdown, Mr McLachlan confirmed.

"With the sewage detections going off in Molong, Mudgee and now Dubbo, I'd say it's a very high likelihood that we have someone in the region that has COVID or multiple people," he said.

"If there is a COVID case identified in the region I'd say there's a very high likelihood that we'll end up in a lockdown situation. We've got to be swift and quick when we know that COVID is in our rural regions."

The state's chief health officer Dr Kerry Chant reiterated the importance of getting tested.

"We are very concerned about regional NSW and that's why we've got some of those protections in place in relation to mask wearing, limited density restrictions.

"We still need to make sure that you are vigilant about signs and symptoms - getting tested, you cannot be complacent, the risk is everywhere," Dr Chant said.

NSW Premier Gladys Berejiklian made the detection announcement at her daily update on Thursday, when it was also announced that the state's Hunter region would go into lockdown.

Premier Berejiklian also confirmed that 20,000 additional Pfizer doses are being sent to regional NSW to replace those doses donated to Year 12 students in Sydney COVID-19 hotspots.

In the Western region, about 1000 people who were booked in for their first dose were impacted.

The new doses will start arriving from August 16.

"That will be incredibly helpful in enabling us to restart some of the vaccination services that have been paused momentarily with the issues of supply of the Pfizer vaccine," Mr McLachlan said.

The drive-through COVID testing clinic is located at Dubbo Showground, and is open on Friday from 8am to 4pm.

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