Victoria's coronavirus case total has grown as the state begins its first day of a five-day lockdown.
The health department said on Saturday a new case was recorded late Friday, taking the total number of cases to 20.
It's not immediately clear if this case is linked to the Melbourne Airport Holiday Inn outbreak which on Friday stood at 13 cases.
From 11.59pm on Friday, Victoria entered a five-day Stage 4 lockdown amid fears the UK variant of Covid-19 was spreading in the community.
Residents will not be allowed to leave their homes except for four reasons: shopping for essentials, caregiving, essential work or education, and exercise for two hours a day.
The five-kilometre limit on travel will also be reimposed as will the compulsory use of masks both indoors and outdoors.
Premier Daniel Andrews called the lockdown a "circuit breaker".
"[The UK strain] is so hyper-infectious, and moves so fast, that it is presenting a very, very real challenge to us," Mr Andrews told reporters on Friday.
"The way in which they are presenting is a very significant concern.
"It is the advice to me that we must assume that there are further cases in the community than we have positive results for, and that it is moving at a velocity that has not been seen anywhere in our country over the course of these last 12 months."
The premier was confident the lockdown, similar to what was imposed in Adelaide, Brisbane and Perth after cases escaped quarantine, would work.
Authorities tracking down Melbourne travellers
Authorities are tracking down 5000 people who passed through Melbourne Airport's Terminal 4 after a case worked at Brunetti cafe while infectious on February 9 between 4.45am and 1.15pm.
About 29 flights arrived and departed through the terminal during that window.
Anyone who visited the terminal then needs to get a test and isolate for 14 days, including those who have since travelled interstate.
The outbreak can be traced back to a family of three who quarantined at the Holiday Inn and are believed to have been infected overseas.
Queensland closes to Greater Melbourne
Queensland responded to the recent outbreak by closing its border to Greater Melbourne from 1am Saturday.
Queensland declared the city a hotspot, and Acting Health Minister Steven Miles said any travellers who have been to Melbourne will be ordered into hotel quarantine.
He said the closure will give contact tracers time to track 1500 people in Queensland linked to the outbreak in Melbourne.
"This hotspot declaration will allow us to get on top of our contact tracing over that five-day period and monitor the situation there. It will allow us to protect Queenslanders and to support our public health officers doing that contract tracing work and not adding to their workload, while they are racing to get to those contacts," Dr Miles said.
The NSW border to Victoria remains open.
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