South Australia is locking out travellers from greater Melbourne after further COVID-19 cases were linked to a hotel quarantine outbreak in Victoria.

The lockout was scheduled to come into effect from 12.01am on Thursday, South Australian time.

Returning SA residents, people relocating and other exempt travellers would still be allowed in but would need to quarantine for 14 days.

“It’s a very dynamic and moving situation,” Police Commissioner Grant Stevens said on Wednesday.

“Our steps in South Australia are taken with an abundance of caution to make sure we’re minimising the risk but at the same time, not taking steps that aren’t deemed to be necessary.

Regional Victoria and cross-border communities are not affected by the planned restrictions.

It comes after two new infections were detected at Melbourne’s Holiday Inn quarantine hotel, bringing the total number of cases linked to the outbreak to eight. They include three workers, two released guests and a family of three no longer staying at the hotel.

Authorities believe a medical device in the family’s room could be to blame for the cluster.

Chief Health Officer Nicola Spurrier said she was “very concerned” by the Victorian outbreak, comparing it to the cluster in South Australia which prompted a snap lockdown.

“We know what happened when we had the Parafield cluster here in South Australia,” she said.

“But on the other hand … we’re in better positions all around Australia. Our contact tracing is much more sophisticated.

I know, because we have very constant conversations with Victoria, that their contact tracing is absolutely fabulous. Their testing is really, really good.”

Victorian Premier Daniel Andrews had earlier cancelled a planned increase in international arrivals to Victoria after even more COVID cases leaked out of the state’s hotel quarantine, saying his government would have “no tolerance for risk” of new strains of the virus.

Two cases were confirmed on Wednesday afternoon, bringing a cluster linked to the Holiday Inn hotel to eight.

Victoria had been due to boost its arrivals cap by 200 from Monday, but now an entire quarantine hotel has been closed for deep-cleaning. Mr Andrews has cancelled the scheduled arrivals increase until more is known about “hyper-infectious” virus variants from South Africa and Britain.

Two further individuals linked to the Holiday Inn Melbourne Airport have tested positive to coronavirus (#COVID19) today: a worker, and a previous resident who exited the facility on February 7. The number of cases linked to the Holiday Inn outbreak is now 8.

— Victorian Department of Health (@VicGovDH) February 10, 2021

“We all have to acknowledge that quarantine and the public health response today must be, by necessity, different than it was a month ago or six months ago,” the Victorian Premier said in Melbourne on Wednesday.

“Because the enemy we are confronting is different than it was a month ago or six months ago.”

Mr Andrews (centre) has called for a “different” virus response. Photo: AAP

The national cabinet agreed just last Friday that NSW, Queensland, South Australia and Victoria would gradually increase their international arrivals and hotel quarantine caps from February 15. The premiers and Prime Minister Scott Morrison had “reaffirmed a shared priority to supporting Australians to return home”.

Victoria had been due to raise its limit from 1120 to 1310 arrivals a week, but that has been scuppered by the hotel quarantine leaks. Two workers at Melbourne Airport’s Holiday Inn tested positive for coronavirus this week, as well as a guest who recently completed a fortnight’s quarantine.

Mr Andrews said the cases have been linked to the British strain of the virus, which is believed to be more transmissible.

“These are highly infectious, hyper-infectious, and it is a very significant cause for concern, not just for us but for every government and public health officials across the country,” he said.

“This is a wicked enemy, made more challenging by the fact that it is changing, it is a moving target.”

Mr Andrews said the new strains worried Victorian authorities, and he wanted “to get to the bottom of what’s going on” before allowing more international travellers in.

The Melbourne Airport Holiday Inn has been closed. Photo: AAP

“We believe it is appropriate to have a very low tolerance, or perhaps no tolerance for risk, particularly risks that you don’t quite understand,” he said.

“We are not taking any risks that would see us have to get to a situation where we ask Victorians to deal with other restrictions. Victorians have given a lot, and I’d just won’t run the risk until we know and understand exactly the nature of the challenge that this changing virus presents to us.”

The Premier said he had informed Mr Morrison of his decision. The New Daily has contacted the PM’s office for comment.

On Wednesday afternoon, the South Australian government announced it would impose a hard border closure on non-residents coming from greater Melbourne, from midnight.

Other concerns have been raised about the new virus strains, including whether the AstraZeneca vaccine will be effective against them; and whether they may have a longer incubation period and require different testing regimes.

Andrews defends hotel quarantine

Only on Tuesday, Mr Andrews boasted of Victoria having “higher standards” of hotel quarantine than NSW, meaning his state wouldn’t ever accept the same number of arrivals as its northern neighbour.

Just hours later, two infections were announced in a special 4.30pm press conference.

“I am very confident we have a system that is worthy of being copied by others. It’s not about boasting, it’s a fact,” Mr Andrews had said on Tuesday.

“If it were anything other than one of the best systems … then I doubt very much any first ministers across the country would have agreed to copy it.”

On Wednesday, Mr Andrews again backed his state’s system, stressing factors such as hotel workers not being allowed to have second jobs, and a ban on private contractors.

CMO Professor Paul Kelly. Photo: AAP

“We are ripping up carpet, for heaven’s sake, and replacing it with vinyl. We test everybody every day, we test them on the days off … and still, this wicked and changing enemy can be a step ahead of you.”

On Tuesday, chief medical officer Professor Paul Kelly said Australia’s hotel quarantine program had catered for 211,000 people. He said it was “very good” but “of course” improvements could be made.

To that end, he said the Australian Health Protection Principal Committee would conduct an end-to-end review of quarantine arrangements.

“The AHPPC, the committee of chief health officers that I chair, have been given the task to relook at everything that we’re doing from end to end,” Professor Kelly said.

“We continue to look at the way that people are transported to quarantine hotels, we’re continuing to look to the procedures and the systems and the safety of our quarantine hotels.”

Another component could be a ‘day 16’ test for arrivals to Australia, following a concerning case in NSW where a returned traveller tested positive days after leaving quarantine.