South Australia recorded just one new COVID-19 case overnight.
The cluster has now reached 20 with Premier Steven Marshall warning there are thousands of more tests being done.
“The good news is that overnight there’s been just one new infection,” Mr Marshall said on ABC radio.
“The advice was go hard and go early, and get on top of this straight away. We can’t let this get away and that’s what we did.
“What I’m pleased about is how quickly we’ve been able to get onto the situation at the moment. We put the net over SA yesterday.
“It’s still early days and there is still an anxious 24-48 hours ahead but the good news is it is a different situation to what we had yesterday morning.”
Due to the dramatic increase in cases Northern Territory, Queensland, Western Australia and Tasmania all closed their borders to South Australia with fears of a Melbourne-like second wave.