Australian Prime Minister Scott Morrison has described strict coronavirus restrictions put in place across Victoria as a "heavy blow" for the country.

Morrison revealed on Thursday that stage 3 and 4 lockdown restrictions in Victoria that took effect on Wednesday night would cost the Australian economy up to 12 billion Australian dollars (8.6 billion U.S. dollars).

With non-essential businesses closed to prevent the spread of COVID-19, Morrison said that it was estimated the increase in effective unemployment to be between 250,000 and 400,000.

"This is a heavy blow, a heavy blow," Morrison told reporters in a press conference in Canberra.

"Eighty percent of this economic cost is expected to be in the affected areas of Victoria.

"The remainder represents a preliminary estimate, and I underline that, of the broader impact on confidence in other states and supply chain impacts from the shutdown of certain industries in Victoria.

"The combined effect on GDP of the stage 3 and 4 Victorian restrictions through the September quarter is expected to be in the order of 10 billion to 12 billion Australian dollars detracting some 2.5 percentage points from quarterly real GDP growth."

Restrictions in Victoria are now the strictest in the country, with about five million residents of metropolitan Melbourne subjected to a curfew between 8 p.m. and 5 a.m. local time.

Also on Thursday, Greg Hunt, the Minister for Health, said that Australians were enduring the "most difficult period in our history."

"We're going to have to go through the most difficult period in our history, I think, arguably the most difficult period because these restrictions are unprecedented," he told Today, an Australian breakfast television program.

"People are being locked in their house by day other than for an hour for shopping or work; people are being locked completely in their houses overnight.

"It is like nothing we've ever experienced and we say it's difficult but this is something that will help us save lives but we'll have to get that tracing done so it's every case, every day, every contact."

His comments came as Australia surpassed 250 coronavirus deaths, with the national toll rising from 247 to 255 between Wednesday and Thursday.

Eight deaths were in Victoria, taking the state's death toll to 170. Four of the eight were linked to outbreaks of the virus in the aged care sector.

Victoria also confirmed 471 new cases in the past 24 hours, compared to a record 725 announced on Wednesday. It brings the state's seven-day average number of daily cases to 537.

"In Victoria at the current time: 2,388 cases may indicate community transmission, 7,449 cases are currently active in Victoria," said a statement from the Department of Health and Human Services in Victoria on Thursday.

Morrison on Thursday acknowledged that the new lockdown would take a toll on Victorians and announced 12 million Australian dollars (8.6 million U.S. dollars) in additional funding for mental health services.

"Mental health and suicide prevention is one of my government's highest priorities," he said.

"For Victorians these last few weeks have been devastating and the loss of freedom that comes from the first lockdown now combined with the second one with the Victorian wave, not being able to connect with friends and loved ones, concerns about employment, all of this takes a toll."