VICTORIA will go into lockdown for seven days from 8pm tonight, with Premier Daniel Andrews saying "we have no choice" but to act now.

As with previous lockdowns, Victorians will be restricted to leaving home for just five reasons - getting food and supplies, exercising for up to two hours, care and caregiving, authorised work or education that cannot be done from home, and getting vaccinated.

The 5km limit will be in place for essential shopping and exercise, and schools will close, except for children of essential workers and vulnerable workers. Childcare centres will remain open.

The lockdown also means community sport will be cancelled this weekend.

According to Mr Andrews, lockdown was the only option to run a burgeoning Melbourne COVID-19 outbreak to ground.

"There are no alternatives to lockdown," he said.

"If you wait, it will spread, and once it spreads, you can never even hope to run alongside it, let alone get out in front of it and bring it back down to zero.

"There is no debate or discussion about this. The Delta variant moves at lightning speed."

Mr Andrews told reporters at a late afternoon press conference the 8pm start was to try to prevent people going out and spreading the virus on Thursday night.

“This evening go home, and begin that lockdown. Don’t be out and about, because all you might be doing is spreading the virus," he said.

The lockdown announcement comes after Victoria recorded mystery COVID-19 cases in the past day, despite initially recording zero new cases yesterday. Traces of COVID-19 were also found in wastewater in Wangaratta, in the state's north-east.

Mr Andrews again urged Victorians to get tested immediately if they had symptoms, given the concern the virus has spread to the regions.

"If you have symptoms you have got COVID-19 - that's what you have to assume," he said.

"That means you have to go and get tested. Don't wait an hour or an afternoon, don't wait days and go to work in the intervening period, you can't do that."