CANBERRA, Dec. 22 (Xinhua) -- Thousands of people in Australia's Northern Territory (NT) have been asked to self-isolate and get tested for coronavirus.

Natasha Fyles, the NT's Health Minister, has urged more than 3,800 people who have travelled to the NT from Sydney since December 11 to get tested immediately in response to a COVID-19 outbreak in the city.

New South Wales (NSW), of which Sydney is the capital, recorded eight locally acquired cases of COVID-19 on Tuesday, and an additional 10 cases in returned travellers in hotel quarantine.

"Investigations continue into the source of the Avalon cluster, which now numbers 90," a statement from NSW Health said on Tuesday.

The NT closed its borders to the Sydney area on Sunday afternoon and Fyles said that the NT's testing capacity has been increased in response to the outbreak.

"We know that this is extremely upsetting, this is difficult and it being so close to Christmas adds to that burden," Fyles said, according to News Corp Australia on Tuesday.

"We will of course work with individuals around their circumstances, upholding those health directions and principles, to make it as easy as possible."

The NT has had the most success preventing the spread of COVID-19 out of any of Australia's eight states and territories.

As of Monday afternoon the NT has had 71 confirmed cases of COVID-19, and it is the only state or territory with no deaths from COVID-19.