Last night, Melbourne entered its third lockdown. And the world watched it live.

At 11:59pm on Friday night, the entire state of Victoria went into a snap five-day lockdown.

And during the Australian Open match between Novak Djokovic and American Taylor Fritz, the rest of the world watched it live.

Midway through the match, fans were escorted out of the Rod Laver Arena at 11.30pm, to make it home in time for the Stage 4 restrictions to kick in.

Image: Getty.

Just finished watching last nights @AustralianOpen At 11:30 PM smack dab in the middle of the fourth set on Rod Laver, all the fans were kicked out as Melbourne is back on full lockdown for five days. Crazy.

— Dan Osborne (@LaziestofDans) February 12, 2021

Surreal scenes at @AustralianOpen with booing fans told to leave the arena midway through a match owing to Covid lockdown in Victoria. This was never going to be a "normal" event but now it's gone to a new level. Felt sorry for crowd but organisers had no choice but to comply.

— FletcherSport (@SportFletcher) February 12, 2021

For the rest of the match, Djokovic and Fritz continued on in an eerily empty arena.

Image: Getty.

The lockdown comes in response to a cluster of COVID-19 cases that have been traced back to a Melbourne quarantine hotel.

As of Saturday morning, there are 20 active cases in the state.

The strain currently active in Victoria has been confirmed as being the UK variant of COVID-19, which Premier Daniel Andrews said: "is moving at a velocity that has not been seen anywhere in our country over the course of the last 12 months."

Sending so much love to everyone in Victoria - you got this 💪🏼 https://t.co/oHOsaQuhXn

— Natalie Forrest (@nat_forrest) February 12, 2021

Announcing the lockdown on Friday, Andrews told media he'd been warned that there are likely already further cases in the community that had yet to be detected.

"The challenge that I have, and the challenge that all of us will have to confront, is that if we wait for this theory - that it might be out there, there might be more cases than we know about - if we wait for that to be proven correct, it will be too late. And then we will face the prospect of being locked down until a vaccination is rolled out. That's not days or weeks, that's months," he said. 

Andrews called the snap lockdown a "circuit breaker" that hopefully will allow the state to get ahead of the virus' spread. 

"We will be able to smother this. We will be able to prevent it getting away from us. I wanna be here on Wednesday next week announcing that these restrictions are coming off, but I can't do it on my own. I need every single Victorian to work with me, and with our team, so that we can run this to ground and we can see this strategy work, just as it has worked against this UK strain in Brisbane and in Perth," Andrews said. 

A reminder of what Victorians can do under Stage 4 restrictions. 

Under stage four restrictions, Daniel Andrews says Victorians will only be able to leave their house for four key reasons, shopping for essential items, essential work, caregiving and exercise. 

Residents will be allowed to leave their homes for two hours of exercise a day with either their household, partner, or one other person. 

Schools will be closed except for essential worker's children, masks must be worn everywhere outside of the home, and you may only travel 5km from your property - unless essential for shopping or essential work. 

No private gatherings are allowed, and everyone who can work from home must do so.

Gyms, pools, community centres, entertainment venues and libraries must all close.

Funerals can only have 10 mourners, and according to the premier's statement "weddings will need to be postponed."

Where did the outbreak start?

A nebuliser — a machine that vaporises liquid for medicinal purposes — used inside the room of an infected family of three at the Holiday Inn hotel is the suspected cause of the outbreak.

The nebuliser was used in the hotel on Wednesday, February 3, and Thursday, February 4, and health authorities are working on the theory the virus spread to others through tiny air particles.

Victorian Chief Health Officer Brett Sutton thinks exposure happened on those two days when the nebuliser was used, "which then meant that the virus was carried out into the corridor and exposed the authorised officer, and the food and beverage service worker and also the other resident."

The person using the nebuliser is now in ICU battling the coronavirus. 

How did it spread?

An authorised officer at the Holiday Inn - a woman in her early 50s - returned a negative swab on Wednesday, February 3, and Thursday, February 4, but started developing symptoms during her shift on Sunday, February 7, and tested positive to COVID-19 the same day.

She visited three locations during the time it's believed she was infectious: Marciano’s Cakes in Maidstone, Dan Murphy’s in Sunshine and Off Ya Tree Watergardens in Taylors Lakes.

A hotel quarantine guest who was staying opposite the family of three left the hotel after her 14-days in isolation on Sunday, February 7, and returned a positive test on Tuesday, February 9. 

Investigators believe she was exposed to the virus just before being tested as she left quarantine on the weekend. 

Two more hotel quarantine workers and a returned traveller then tested positive mid-week.

Anyone who visited these locations must isolate, test and remain isolated for 14 days. For a full list of exposure sites and locations where you can get a #COVID19 test, visit: https://t.co/JAVfgx4HMg #COVID19Vic

— VicGovDH (@VicGovDH) February 12, 2021

As of Saturday morning, there are a total of 20 confirmed cases linked to the outbreak, with 20,166 tests conducted in the past 24 hours.

There are fears Victoria's COVID-19 outbreak could have spread interstate after an infected person spent more than eight hours at an airport cafe. 

The Brunetti cafe in Terminal 4 at Melbourne Airport was listed as an exposure site early Friday morning, after being visited by the case on February 9 between 4:45am and 1:15pm. 

It brings the total number of exposure sites listed on the Health Department's website to 30, with the number of cases growing to 13.

What about the Australian Open?

The Australian Open will continue without crowds. 

More than 1000 international players, coaches and media are currently taking part in the tournament being held at Melbourne Park in the CBD.

How are the other states and territories reacting to the cluster?

The cluster has prompted several states to tighten borders to travellers from Greater Melbourne.

South Australia locked out travellers from the Victorian capital at midnight on Thursday, while Queensland barred entry to visitors of the city's exposure sites from 1am on Saturday.

Western Australia and Tasmania announced its hard border to Victoria would be extended for at least another seven days.

In New South Wales, borders are still open but anyone who arrived home after 11:59pm on Friday, February 12, must stay at home for five days.

- With AAP

Feature image: AAP/Getty.