South Australia, home to around 1.7 million people, joined Victoria and parts of New South Wales (NSW) in fresh restrictions aimed at tackling breakouts of the virus.
Australia was initially lauded around the world for its tough stance on preventing Covid transmission as it closed borders and banned travel.
But its inoculation programme has been dismal and people are angry that lockdowns are being imposed again more than a year into the pandemic.
Just over 10 per cent of the population are double-jabbed, according to Our World in Data. It puts Australia behind Colombia, Mexico, Malaysia and Morocco, the figures show.
The UK, Spain and Canada are in the top three spots on 53.1 per cent, 52 per cent and 50 per cent respectively.
Speaking at a press conference on Wednesday, Mr Morrison said he accepted responsibility for the “regrettable” problems with the vaccine rollout.
When asked if he would say sorry for the issues, he replied: "We all know they’re [the delays] the result of many factors.
"There is going to be plenty of critics and hindsight. They will have various motivations for doing that."
He added: "I take responsibility for the problems that we have had, but I am also taking responsibility for the solutions we’re putting in place and the vaccination rates that we are now achieving."
Jim Chalmers, a Labour Party frontbencher, said: "This is a prime minister who hides while people hurt."
Tuesday's new lockdown means around half of Australia's population is now locked down.
NSW and Victoria, the two largest states, reported sharp increases in new cases on Wednesday, a blow to hopes that lockdown restrictions would be lifted soon.
NSW, home to the country's most populous city Sydney, reported 110 new cases, up from 78 the day before, nearly four weeks into a lockdown of the city and surrounding areas to contain an outbreak of the Delta variant.
Victoria state clocked 22 new cases, up from nine the day before - its biggest increase since the outbreak began this month.
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