Health authorities in NSW are on alert for further COVID cases after coronavirus fragments were detected in a sewer system that services tens of thousands of people in Sydney.

On Friday morning, NSW Health flagged the detection of the virus fragments at a sewage network site at Homebush in Sydney.

NSW Health said several returned overseas travellers who recently tested positive for COVID-19 live in this catchment.

“People who are recently recovered from COVID-19 can continue to shed virus fragments into the sewerage system for several weeks even after they are no longer infectious,” it said.

The sewage network site at Homebush collectively services about 40,500 people in 15 suburbs.

Residents are being urged to “be vigilant in monitoring” for “even the mildest of cold-like symptoms”, and get tested and isolate immediately until a negative result is returned.

Tweet from @NSWHealth

The alert to monitor for symptoms applies to the suburbs of Homebush West, Strathfield, Rookwood, Concord West, Sydney Olympic Park, Wentworth Point, Newington, Lidcombe, Homebush, Silverwater, Petersham, Liberty Grove, Rhodes, North Strathfield and Concord.

No new locally acquired coronavirus cases were recorded within NSW overnight in the 24 hours to 8pm on Thursday, and no new cases were detected in hotel quarantine.

The detection of COVID-19 particles comes after the NSW government said 25 Pfizer sites across the state are now taking bookings for people aged 40 to 49.

State health authorities said it had been regularly exceeding its target of 60,000 vaccination jabs per week, half of which were administered at its mass vaccination hub at Sydney Olympic Park.

NSW Health also said in its daily update on COVID-19 cases that the state was currently treating 51 infected people, one of whom is on a ventilator in intensive care.

“Most cases (96 per cent) are being treated in non-acute, out-of-hospital care, including returned travellers in the Special Health Accommodation,” it said.