Authorities on Tuesday ordered the lockdown of 36 suburbs in Australia's second biggest city Melbourne in an attempt to stop a spike in coronavius cases, a dramatic departure from the relaxation of restrictions elsewhere in the country.

From midnight on Wednesday the first suburb-specific stay-home order will be imposed on some 320,000 people, the Victorian state Premier Daniel Andrews told a news conference on Tuesday.

Residents in the suburbs must stay home unless travelling for work, school, healthcare, exercise or food for a period of four weeks.

Cafes and restaurants would have to revert to takeaway only, just weeks after they returned to seated diners amid a wider reopening of the national economy.

The Victorian state government requested all flights be diverted to other states to prevent the risk of imported cases.

"If we don't take these steps now we will finish up in a situation (where rather) than locking down 10 postcodes, we will be locking down every postcode," said Andrews, referring to postal codes which cover the 36 suburbs.

"People are desperate for this to be over, no one more than me, but it isn't and pretending won't get us to the other side."

The return to lockdown is a devastating setback for the home state of nearly a quarter of Australia's 25 million people, widely seen to have taken one of the toughest enforcement approaches when the country first went into lockdown in March.

But while most other Australian states have reported zero or low single-digit daily increases in COVID-19 infections for weeks, Victoria has experienced double-digit increases for each of the previous 14 days, taking the national total to its highest number of new cases since April.

In the 24 hours to Tuesday, Victoria reported 64 new cases, down from the previous day's 75 new cases. By comparison, the most populous state, neighbouring New South Wales, and the third-most populous, Queensland, both reported no new cases. The country has had 104 deaths from about 7,800 infections.

The Victorian government is receiving help from defence personnel and healthcare workers sent from interstate, with teams door-knocking in affected neighborhoods to ask people to undertake tests for the illness, Andrews said.

Police in the lockdown suburbs will fine people who broke the rules, he said.

"We've been through this before and we now have to go through it again," Lambros Tapinos, the mayor of several affected postcodes told Reuters by telephone.

"It will be a devastating impact on people and particularly local businesses, but we have to do it," he added.

REOPENING WITH CONDITIONS

The reversal is at odds with moves taken by neighbouring South Australia and the northern state of Queensland which both unveiled plans to reopen internal borders to the rest of the country except Victoria, citing its infection numbers.

"We have worked so hard to get ourselves into a very enviable position and we are not prepared to go backwards," South Australia state premier Steven Marshall told reporters.

Queensland said it would reopen its border to the rest of the country from July 10 while keeping out arrivals from Victoria.

Queensland does not share a border with Victoria but would make people entering from other states sign a declaration that they had not been to Victoria for 14 days with the threat of a A$4,000 ($2,738) fine if they were caught lying.

NSW, which borders Victoria, said it would continue to keep its border open as it focused on supporting its economy amid the pandemic.