SYDNEY/MELBOURNE - Australian police set up suburban checkpoints in coronavirus hotspots in Melbourne on Thursday and were considering using drones to enforce stay-at-home orders as authorities struggled to contain new outbreaks in the country's second-largest city.

More than 1,000 police set up posts around 36 suburbs, which returned to lockdown after a spike in new infections.

While the rest of Australia opened state borders and loosened social distancing restrictions, Melbourne's state of Victoria promised to fine those in the affected zones that breached curbs on non-essential movement.

Victoria reported 77 new cases, up slightly from the previous day and in line with weeks of double-digit daily increases.

The state government has also commenced an inquiry into enforcement of hotel quarantine for people returning from overseas amid worries some new infections came from people who had dodged the mandatory two-week isolation.

"I'm obviously concerned about the outbreak, and I'm pleased that the premier has taken the action he's taken by putting in place the lockdown for the outbreak in those suburbs," Prime Minister Scott Morrison said in a televised news conference, referring to the Victorian state government.

"We have seen some levelling (in new cases) although they remain at elevated levels and that is of concern and that means as the lockdown now is in place, we would hope to see those numbers fall again."

Victoria police commissioner Shane Patton promised a heavy presence in "high-volume public places" and said police may even use drones to track down people travelling for reasons other than work, school, healthcare and grocery shopping.

"People will not know where we will be, they will not know how long we'll be there for, but they'll be intercepted," he said.

Australia has fared better than many countries in the pandemic, with around 8,000 cases and 104 deaths. However, the recent jump in Victoria has stoked fears of a second wave of COVID-19, echoing concerns expressed in other countries.

Most states have said they will reopen their internal borders except to Victoria. Neighbouring New South Wales (NSW), the most populous state, has kept its border open except to people arriving from the targeted Victorian suburbs.

A director at Phat Milk cafe in Melbourne's Travancore, one of the affected suburbs, said the sudden return to lockdown had left him with a kitchen full of food.

"What do you do with that stock You have to close the kitchen because it's takeaway," said the director, who gave only his first name, Hach.

"From four to six staff, you only have one staff on. It is hard, but you just got to find the passion, the drive, and be a bit creative and hang in there."

WEAK LINK

The Victorian outbreak has raised concerns about the efficacy of the state's quarantine procedures.

In neighbouring New South Wales, supermarket chain Woolworths Group WOW.AX put 50 staff at a Sydney store into isolation after a worker tested positive to the virus despite clearing a mandatory two-week quarantine in Victoria, authorities said.

Meanwhile, remote Northern Territory reported its first infection in two months after a traveler who had entered the country via Melbourne and completed quarantine showed symptoms after returning to his home territory.

"People will be anxious hearing this news ... but we have measures in place to protect our community (and) these measures have been followed," Northern Territory Health Minister Natasha Fyles told reporters.

The infected person, aged in their 30s, has been isolated in hospital, she added.

Globally, coronavirus cases exceeded 10 million on Sunday, a major milestone in the spread of a disease that has killed more than half a million people in seven months.

(Reporting by Byron Kaye and Melanie Burton; Editing by Sam Holmes) ((byron.kaye@thomsonreuters.com; +612 9321 8164; @byronkaye;))