NSW Health said there were five coronavirus cases diagnosed in returned travellers in hotel quarantine in the 23,236 tests undertaken in the 24-hours to 8pm on Wednesday.

Deputy Chief Officer Jeremy McAnulty said on Thursday 71 patients were being treated in NSW and none of them were in intensive care.

Fragments of the virus had been detected at sewage pumping stations serving nearly 25,000 people in Bowral and Moss Vale and while there had been recent cases in Moss Vale, there were no recent cases reported in Bowral.

More than 18,500 western Sydney residents have been alerted to the presence of the virus in sewage at two local sewage pumping stations.

Affected suburbs include North Kellyville, Rouse Hill, Box Hill, The Ponds, Kellyville Ridge, Parklea, Quakers Hill and Acacia Gardens.

"Everyone in these areas is urged to immediately get tested if they have any symptoms at all that could signal COVID-19," Dr McAnulty said.

While detection in sewage samples could reflect the presence of older cases in those areas, there could be other active cases in the local community in people who had not been tested and assumed their symptoms were just a cold.

Australian Associated Press