Deputy Prime Minister Michael McCormack has railed against border closures as states shut down travel with South Australia over a coronavirus cluster.

The Adelaide cluster has infected 20 people in the city’s north, sparking concerns the virus could spiral out of control.

Another confirmed case is still being investigated and health officials have also identified another 14 people who are considered at high risk of having the virus.

Queensland, the Northern Territory, Tasmania and WA have slammed the gates shut on SA.

NSW is telling people to delay travel to the state, while Victoria has asked for South Australians to cancel all non-essential travel.

The two most populous states have left their borders open and ramped up screening of Adelaide arrivals.

Mr McCormack said there was no need for internal border restrictions with families looking to reunite over Christmas.

“What we need now is we do need businesses to reopen,” he told the Nine Network on Wednesday.

“We do need Australians to get back to work and we do need those borders to be open.”

Border closures have been a thorn in federal-state relations throughout the pandemic.

Simon Birmingham, the most senior South Australian federal government minister, praised the state’s response.

“The locals are nervous, it’s safe to say, these are challenging times for SA and everybody is on edge as to exactly what will unfold,” he told ABC radio.

The tourism minister said a huge testing, contact tracing and isolation effort was under way with 4000 locked down in their homes.

“That gives us the best possible chance of successfully suppressing COVID in this state,” Senator Birmingham said.

About 100 Australian Defence Force troops are on the ground assisting authorities desperately trying to prevent a serious outbreak.

The Adelaide cluster has prompted doctors to urge a cautious approach on returning to the workplace in other parts of the country.

Australian Medical Association president Omar Khorshid said it was too soon for a mass return to workplaces and public transport.

“The only way to keep these numbers low is to continue to follow the habits that have proven so effective in getting Australia to such an enviable position,” he said.

Dr Khorshid said workplaces were one of the main places where coronavirus spreads.

“Working from home minimises the possibility of workplace transmission, reduces the geographic spread of the virus and makes our public transport systems safer,” he said.

Victoria has now notched 19 days without a new coronavirus case.

ACT has recorded a rare infection, with a diplomat in quarantine testing positive for the disease.