Canberra, July 21 : Anger is growing in Australia as 13 million people -- about half the nation's population, endure fresh lockdowns to deal with the Covid-19 outbreaks. Many people have expressed frustration at being back in the highly policed lockdowns 18 months into the pandemic. A third state, South Australia, joined Victoria and parts of New South Wales in lockdown on Tuesday. Fewer than 14 per cent of Australians are vaccinated - the worst rating among OECD nations, the BBC reported. Australia's two biggest cities, Sydney and Melbourne, are among places facing uncertainty over when to re-open. Re-openings in the UK and the US have increased pressure on the federal government. Prime Minister Scott Morrison has been heavily criticised over the slow vaccination rate, but has resisted calls to apologise. "No country has got their pandemic response 100 per cent. I think Australians understand that," he told reporters on Wednesday. He again cited Australia's success in keeping overall infections well below many nations. It has recorded 915 deaths. Morrison noted that the UK had seen over 90 deaths in a single day on Tuesday. But Labor frontbencher Jim Chalmers said: "This is a prime minister who hides while people hurt." Until recently, Australia had been largely praised for its strategy of border closures, quarantine programmes and snap lockdowns. But the highly contagious Delta variant has challenged these defences in the past month. The outbreak in Sydney - Australia's largest city - has infected more than 1,500 people. Officials reported 110 new cases on Wednesday, despite the city's fourth week of lockdown. Residents must not leave their homes except for grocery shopping, exercise and other essential reasons. There are fears Sydney's lockdown could extend into September, after modelling showed the city may be months from eliminating cases. South Australians will endure seven days at home after five cases of the Delta variant were found. Victoria -- which saw 22 new infections on Wednesday -- will keep its lockdown until at least Tuesday. /IANS