By Tania Lee

MELBOURNE, July 8 (AFP) — Shoppers in Australia's second-biggest city stripped supermarket shelves Wednesday as millions in Melbourne prepared for a return to virus lockdown, with warnings the new restrictions could prompt a mental health crisis.

Five million residents were ordered back into a six-week lockdown beginning midnight Wednesday into Thursday as soaring community transmission of the coronavirus brings more than 100 new cases daily.

A further 134 infections were detected in the past 24 hours — small in comparison to the tens of thousands in hard-hit countries such as the US and Brazil, but considered a major spike in Australia, which had otherwise been successful in containing COVID-19.

The country's largest supermarket chain, Woolworths, said it had reimposed buying limits on items including pasta, vegetables and sugar after shoppers rushed to stores across Victoria state.

Experts have warned that people everywhere will have to get used to the "new normal" of on-and-off restrictions as new clusters emerge and subside, while there are also concerns over the economic and mental health impacts the measures will bring.

"As frustrating as it is I support (the lockdown) — but ask me again in six weeks," stoic Melbourne resident Michael Albert told AFP. 

Treasurer Josh Frydenberg said the Melbourne lockdown would cost the economy up to Aus$1 billion ($700 million) a week, telling public broadcaster ABC the burden would "fall heavily on businesses".

"This is not the situation that anybody wanted to be in, but it is the reality that we must confront," said state Premier Daniel Andrews.

Restaurants and cafes will be limited to serving takeaway food, while gyms, beauty salons and cinemas will be forced to close again.

Residents will be restricted to their homes except for work, exercise, medical care or to buy essentials — a return to social isolation that was only recently lifted.

Professor Michael Kyrios, a clinical psychologist at Flinders University, warned that Victoria needed to brace for a "coming mental health crisis" as a result.

Guards replaced

"This will likely place the mental health care system in a precarious situation with very limited ability to mobilise resources in response to the increased incidence of mental illness arising from the COVID crisis," he said.

Health authorities say they have linked many of the Melbourne coronavirus cases to hotels where residents returning from overseas were being quarantined. 

Local media reported security guards had breached infection control regulations — including allegedly having sex with guests held in isolation — prompting the government to replace the private contractors with prison staff and launch an inquiry.

Australian Prime Minister Scott Morrison said the country was now considering limiting the number of citizens returning from abroad, afterVictoria began diverting international flights to other cities to ease the burden on its quarantine facilities.

"There is a volume that can be accommodated by the (other) states and territories currently, but they certainly wouldn't want to see that increase," he told reporters in Canberra.

Thousands of health workers are knocking on doors in the worst-affected areas of Melbourne urging residents to get tested for coronavirus, with officials saying about 10,000 people have refused after being influenced by online disinformation.

Around 3,000 people in the city have already been locked inside their homes since Saturday in Australia's strictest coronavirus response to date after a cluster emerged in a high-rise public housing estate.

A total of 75 cases have been detected in the densely populated towers during a major testing blitz.

Long queues of cars were backed up at Victoria's border Wednesday after neighbouring New South Wales closed the boundary for the first time in the pandemic — essentially sealing off the state from the rest of Australia.

The hastily announced decision left residents of border towns scrambling to obtain permits to cross for work or other essential reasons, while school holiday travellers were rushing to return home.

Police checkpoints have been set up at major road crossings and drones are monitoring large sections of the vast border, with one man arrested Wednesday after allegedly attempting to cross illegally.

Australia has recorded almost 9,000 cases of coronavirus and 106 deaths.