Cowra in central western NSW is going into lockdown after a school boy there was diagnosed with COVID-19 and traces of the virus were found in wastewater.

The central western NSW town of Cowra is going into lockdown after a primary school boy tested positive to COVID-19 - its first case in the entire pandemic.

Chief Health Officer Kerry Chant said the week-long lockdown in the town of about 10,000 people would come into force at 5pm on Monday.

"Anyone who was in Cowra from 13 September regardless of where they are, must adhere to the stay-at-home requirements," she said on Monday.

"There was a nine-year-old boy who attended school in Cowra and there were a number of associated community exposures."

The source of the case remains under investigation, but health authorities fear there are other cases circulating in the community, with fragments of the virus that causes COVID-19 detected in the town's wastewater last week.

"We're really cautious that this might not be the case that was triggering the sewerage testing earlier on," Western NSW local health district chief executive Scott McLachlan said.

"This family doesn't live in Cowra - they live outside of Cowra.

"So I really would urge some caution for everyone... if you've got any sort of symptoms, please, most urgently, come and get tested, even if you don't have symptoms."

NSW Health also has concerns about the far western town of Dareton, where traces of the virus have been detected in sewage.

Everyone in this area is urged to monitor for the onset of symptoms, and if they appear, to immediately be tested and isolate until a negative result is received.

Last week Lismore, near the Queensland border, Albury on the Victorian border and Glen Innes in the northern tablelands went into a seven day lockdown after COVID-19 cases were recorded in those communities.

Of the 935 locally acquired cases reported in NSW to 8pm on Sunday: 49 are from the Nepean Blue Mountains district, 45 are from Illawarra Shoalhaven, 24 are from the Hunter New England district, 19 are from Central Coast, 10 are from western NSW, seven are from the Southern NSW Local Health District, two are from far west, three are from the Murrumbidgee Local Health District and 10 are in jails.