South Australia's COVID-19 cluster has grown to six and more exposure sites have been revealed but the state still has a chance to "nip this in the bud", Premier Steven Marshall says.
The one new case is linked to an Adelaide restaurant where a birthday party was held at the weekend, which authorities fear could become a superspreader event.
The woman in her 20s was working at The Greek restaurant and also works at the Westminster School, where she attended teacher training on Monday.
However, students had not returned from school holidays.
The premier has also revealed the state government will extend income assistance to people statewide on top of federal assistance for those missing out on work in Adelaide.
Payments of up to $600 a week will be available for those who are losing work. Mr Marshall thanked South Australians for abiding by lockdown rules and getting tested in record numbers.
"We've got one shot to stop this outbreak dead in its tracks," Mr Marshall said on Wednesday.
"We've got a chance to nip this in the bud. We don't want to have an extended lockdown in South Australia."
The premier said officials were "pulling every single lever possible" to increase testing capacity amid continued reports of long lines and long waits at testing centres.
"We don't want people angry and frustrated with delays. We are ramping up capacity across testing sites," he said.
"We're doing our very best to massively increase that capacity today." SA's list of exposure sites has grown to more than 50 and includes major shopping centres and schools.
Chief Public Health Officer Nicola Spurrier said SA Health now had two sites of most concern, The Greek restaurant and the Tenafeate Creek winery at Yattalunga, north of Adelaide.
She said almost 6000 people linked to all 52 exposure sites were now in home quarantine.
SA's virus cluster is linked to an 81-year-old man who recently arrived in Australia from Argentina and quarantined in Sydney before travelling to Adelaide where he tested positive.
Genomic testing has confirmed the man became infected while in Sydney, not while in Argentina.
During the week-long lockdown, which started on Tuesday evening, South Australians will only be allowed out for five reasons - to provide essential care, to seek medical assistance, to buy essential food and other goods, for essential work, or to exercise for up to two-and-a-half hours.
They must also wear masks when outside their homes.
Schools have closed along with most retail outlets and all construction work has ceased.