Melbourne, May 27 (IANS): Health authorities struggling to contain a fresh Covid outbreak in the Australian state of Victoria have imposed a seven-day lockdown from midnight Thursday.

The state-wide restrictions, announced by the state's Acting Premier James Merlino on Thursday morning, followed a cluster of 26 new local cases centred around the capital city of Melbourne this week, reports Xinhua news agency.

One of those cases is now in intensive care in hospital and on a ventilator.

The "circuit-breaker" restrictions, which will be in place until 11.59 p.m. on June 3, include the compulsory wearing of face masks except at home, and the closure of schools, except to care for the children of essential workers.

Supermarkets and banks will remain open but cafes will be limited to take-away.

Victorians will need five reasons to leave their homes including food and supplies, care giving, authorised work, exercising for two hours with another person (within 5 km from home) or getting vaccinated.

Merlino said it was essential to act decisively, saying "unless something drastic happens, this will become increasingly uncontrollable".

"If we make the wrong choice now, if we wait too long, this thing will get away from us," he said.

The outbreak was detected on Monday when four members of the same family from Whittlesea in north Melbourne tested positive and then on Tuesday a man with connections to that family was also found to be infected.

Genomic testing has connected the cluster to a case of the Indian strain of the virus earlier this month at a quarantine hotel from the neighbouring state of South Australia (SA).

Authorities, however, have yet to locate the "missing link" connecting the SA case to the Melbourne family.

As of Thursday, contract tracers had listed almost 80 exposure sites where at least one of the infected people had visited.

One helpful consequence of the outbreak is that there has been an upsurge in Victorians getting vaccinated with 15,858 people receiving their jab on Tuesday, whereas the previous average daily uptake was less than 6,300.

That figure should now increase with Merlino announcing on Thursday that every Victorian aged 40 to 49 would be immediately eligible for the Pfizer vaccine, while those aged over 50 would still be offered the AstraZeneca vaccine.

"We need you to make a booking, so I really encourage everyone, if you are eligible, get vaccinated," he said.

Meanwhile, authorities in other Australian states and territories have responded to the growing Victorian crisis.

Queensland and SA have closed their borders to more than 200,000 people from Whittlesea, while Western Australia on Thursday banned Victorians from entering the state unless they can obtain an exemption.

New South Wales has closed its border to non-residents who have visited exposure sites and Tasmania has banned anyone who has visited the exposure sites to travel to the island state unless they are classified as being essential travellers.