Australia's Victoria state headed into a seven-day lockdown Friday and criticisms from business and opposition critics began pouring in.

"Businesses are still reeling from the February snap lockdown and many are only just getting back on their feet. The treasurer should have done the work to ensure that businesses can be supported through another lockdown," Victoria's opposition treasury spokeswoman Louise Staley said in a statement Friday.

"Yet again Labor has turned its back on Victorian businesses." 

Australia's second most populous state imposed a seven-day "circuit-breaker lockdown" after four new locally acquired COVID-19 cases were reported, news reports said.

The hard lockdown affects almost 7 million people and aims to contain an increasing coronavirus outbreak in state capital Melbourne, which the federal government has declared a hot spot, The Associated Press reported.

"It's just very difficult," resident Gavin Catt told Agence France-Presse. "This lockdown is affecting us. Many families and friends can't work."

Melbournians have been ordered to stay at home for seven days to stall transmission and buy the authorities time to investigate how the virus again jumped from hotel quarantine into the community.

People will be permitted to leave their homes for health care, essential work, grocery shopping or to get a coronavirus vaccination only.

Australia has recorded 30,000 COVID-19 cases and fewer than a thousand deaths after implementing an aggressive measure against outbreaks.

"We've seen more evidence we're dealing with a highly infectious strain of the virus, a variant of concern, which is running faster than we've ever recorded," Reuters quoted Victoria's acting Premier James Merlino as saying at a news briefing in Melbourne.

He called for military help with the investigation and blamed sluggish vaccine rollout and hotel quarantine failures for the latest outbreak. A new cluster of the virus was detected in Melbourne after a traveler from India became infected while in isolation at a hotel upon arriving earlier this month, The Associated Press said.

Australia's health officials had earlier reinstated pandemic restrictions for Melbourne - limiting sizes of public gatherings and making face masks mandatory in hotels, restaurants and other indoor locations until June 4.

Greg Hunt, Australia's national health minister, said the lockdown was "highly regrettable" but nevertheless "necessary" considering the current circumstances, according to The Hill.

Victoria endured one of the world's most rigid and extended lockdowns last year to contain a second wave of COVID-19 that claimed the lives of more than 800 people in the state - or about 90% of all Australian fatalities.

Meanwhile, a new report says almost 20 nations where COVID-19 is rampant are at risk of running out of oxygen supplies.

Research by the Bureau of Investigative Journalism found critical oxygen shortages in India, Iran, Colombia, Argentina, Nepal, South Africa, Pakistan and elsewhere.