A previously-announced venue of concern initially listed as a casual contact site has also been upgraded to a close contact site after further investigations overnight.

It comes as four people from Young are being treated for COVID-19 in Wagga Base Hospital, Albury and Hilltops residents endure another lockdown, and fragments of COVID-19 were discovered in sewage surveillance in Griffith and Balranald at the weekend.

The Murrumbidgee Local Health District [MLHD] revealed two men and a woman from the Hilltops local government area [LGA] have been diagnosed with the virus late on Sunday.

A woman aged in her 70s has been transferred to Wagga Base Hospital, the MLHD said, and a man in his 40s who is a household contacts has also tested positive for the virus.

A man in his 50s is the third new case to be announced on Sunday night, and all three will be included in NSW Health's formal figures on Monday.

IN OTHER NEWS:

Four new exposure sites in Young have been listed as casual contact sites as contact tracers continue to investigate venues of concern.

Anyone who has visited any of these locations at the listed time is a casual contact and must seek a COVID-19 test immediately, then isolate until a negative result is received:

There are now seven active cases of COVID-19 from the Hilltops LGA, and three people from the Albury LGA have contracted the virus.

Previously announced casual contact venues of concern in young include:

Five people from Young are being cared for in Wagga Base Hospital, and one of the Albury patients has been transferred to Melbourne.

The remaining two are in special health accommodation and isolating at home, MLHD said.

"We ask communities in the areas of Hilltops LGA and Albury LGA to be vigilant with mask wearing, hand hygiene and social distancing, get tested if they have the mildest of symptoms, and if eligible, come forward for vaccination as soon as possible," the authority urged on Sunday night.

The Boorowa Hotel, also known as Top Pub, has been upgraded to a close contact venue since it was announced as a casual exposure site on Saturday.

"This venue is not associated with any of the seven cases who were in Hilltops LGA when diagnosed," MLHD said in a statement.

"The venue was visited by a person from outside the district who later tested positive to COVID-19 and is now isolating outside of MLHD."

Anyone who visited the hotel at 37 Marsden Street between 11am and 12.30pm on Saturday, September 11 must get tested and isolate for 14 days regardless of the result.

Hilltops mayor Brian Ingram said thousands of people had turned out for testing across the LGA at the weekend, while Griffith's leader John Dal Broi said his community is on alert and urged everyone to get vaccinated.

"You'd like to think it's someone just passing through, but we just don't know," Cr Dal Broi said.

"We can't shy away from it, we've just got to accept it and do what we can."

Extra testing is available on Monday in Young, Harden, Boorowa, Cootamundra, Temora and Albury, the MLHD advises.

People can get tested at the following locations, and appointments are not necessary unless specified:

For additional testing locations go to www.mlhd.nsw.gov.au, or for help accessing a test call the Murrumbidgee COVID-19 Hotline 1800 831 099.

We have removed our paywall from our stories which contain need-to-know information about coronavirus. If you would like to support our journalists you can subscribe here.