The Australian state of Victoria will enter lockdown for a third time in a bid to suppress an outbreak of the UK strain of coronavirus.

Officials this week found 13 cases stemming from a quarantine worker who became infected at a Melbourne hotel.

The lockdown will begin on Friday midnight and end on Wednesday.

However, the government has said the Australian Open tennis tournament would continue in the state's capital, Melbourne.

Spectators will be banned from attending the event from Saturday, which had previously allowed up to 30,000 visitors a day. Tickets will be refunded, tournament director Craig Tiley said.

Victorian Premier Daniel Andrews said the current outbreak was not linked to the quarantine hotels used by the tennis players.

He stressed that a "circuit breaker" was needed to combat the "hyper-infectious" strain which he said had likely already seeded other infections in the community.

"This is the fastest-moving, most infectious strain of coronavirus that we have seen," he said, adding that almost 1,000 close contacts had already been reached.

Prior to this outbreak, Victoria had not seen a local infection for 28 days and the state had largely eliminated the virus.

Many Melbourne residents have expressed dismay but also resignation over the retreat into lockdown again.

Last year, in Australia's winter, the city endured one of the world's longest and strictest lockdowns to overcome a second wave which led to more than 90% of Australia's 29,000 cases and 909 deaths.

"We've built something precious, and we have to make difficult decisions, and do difficult things, in order to defend what we've built," Mr Andrews said.

"I am confident that this short, sharp circuit breaker will be effective. We will be able to smother this."

The state will be under the following restrictions for five days:

People must stay at home except for shopping, exercise, caregiving and essential work needs
No gatherings allowed
Travel is restricted to within 5km (3.1 miles) of the home
Mask wearing is mandatory in public
Places of worship and all non-essential venues are closed
Schools are closed except for children of essential workers

Meanwhile, South Australia, Queensland and Western Australia have announced travel bans on people from Melbourne. Further border closures are expected. International flights to Melbourne will also be cancelled, authorities said.

The tough ride continues for the Australian Open as Covid and controversy strike again.

When I was there reporting on the event's opening weekend, the tennis fans I spoke to said how happy they were for sport to have come back to Melbourne.

"We're just grateful," one fan, Angela, told me as she walked around the park. "We know how much this is worth. We know how much we've struggled to achieve that."

The city went through a traumatic, lengthy lockdown last July after a quarantine breach led to more than 18,000 cases.

Now the city is going back into lockdown again and for many it's a dispiriting déjà vu.

Confined to their homes, they're also asking why the tennis is still going ahead.

Why will players and their teams get to move around and play matches while the people of Melbourne will have to stay home

Questions over quarantine

Melbourne becomes the fourth Australian city - joining Perth, Brisbane and Adelaide - to enter a snap lockdown since November.

In each situation, the cases have occurred due to a quarantine hotel breach - with all but one of these found to be the more infectious UK variant.

Victorian health authorities have been scrambling to find out how the virus leaked out, with particular focus being paid to airborne transmission.

Officials say the UK variant is "hyper-infectious". But experts in the past week have questioned why stronger aerosol protections weren't in place when the threat of airborne transmission was previously known.