Concerns raised over eight Sydney suburbs including Berowra, Cowan and Hornsby

Several suburbs have been put on notice after fragments of coronavirus were detected in their wastewater, sparking concern of undetected cases.

Eight suburbs have been put on alert after sewage surveillance sparked fresh concerns of undetected COVID-19 cases in Sydney’s outer northern suburbs.

Sewage being monitored at a plant in the Hornsby Heights area picked up fragment of COVID-19 in suburbs which include Berowra, Cowan, Berowra Heights, Hornsby Heights, Mount Colah, Mount Kuring-Gai, Asquith and Hornsby.

“NSW Health is aware of recent cases in this area, but is concerned that there may be undetected cases,” a release read on Thursday.

“Everyone in the area is asked to be alert for symptoms and to get tested immediately if they appear.”

NSW chief health officer, Dr Kerry Chant, revealed 10 new cases of COVID-19 had been recorded overnight with five of those linked to the Avalon cluster. That cluster has now reached 144 cases.

Health officials confirmed they are also monitoring the northern part of Sydney.

“We have five cases linked to the Avalon cluster today including two cases are close contacts to a person in northern Sydney who is reported yesterday and now linked to this cluster along with his two close contacts recorded today,” Dr Chant said.

Greater Sydney will be restricted to having five people gather inside homes tonight as the city deals with a fresh COVID-19 outbreak. Picture: Jonathan Ng

Further down the coast, Wollongong will also be closely watched during the next two days following a positive case detected in the region on Monday.

“In terms of Wollongong, I think we'll have a better picture over the next 24 to 48 hours but we can’t give the all clear until we have a significant period of time where we are absolutely confident that there’s been no community chains of transmission,” Dr Chant said.

Of the 10 cases reported overnight, three were linked to the Croydon cluster which remains unlinked.

The three new cases were close contacts of six cases reported yesterday and there are now nine cases in that cluster.

One locally acquired case was a close contact of one of the two patient transport drivers reported previously and a further case, from western Sydney, is under investigation.