Australian authorities conducted mass tests and about 4,000 people were confined to quarantine in the hope of stifling a new cluster of cases of the novel coronavirus after hopes it had been largely eradicated.

The state of South Australia reimposed social distancing restrictions on Monday after detecting 21 cases of the coronavirus, most of which were acquired locally, Reuters reported.

The cases were the first local transmissions of the virus in Australia in nine days.

South Australia Premier Steven Marshall said testing had identified five new cases in the past 24 hours, while 14 people were suspected to be infected and were awaiting test results.

“We are not out of the woods. We are just at the beginning stages of dealing with this particular very nasty cluster,” Marshall told reporters in Adelaide.