A mask mandate in malls has been introduced as part of a range of measures by Victoria to suppress another outbreak of Covid-19 in the state. 

In an order made last night, fitted masks must be worn by anyone aged 12 or over in all indoor venues, including shopping centres, workspaces and on public transport. 

“These additional measures are about keeping Victorians safe while our coronavirus detectives work to track down any additional cases and stamp out the spread of this deadly virus,” said acting premier James Merlino. 

“If you’re eligible to get vaccinated, don’t wait. Make an appointment or walk up to a vaccination site today. It’s the best way to protect yourself and your family.”

The Melbourne-based Covid-19 cluster has grown to 15 in just three days and health officials are concerned that one of those people had attended an AFL match on Sunday where 23,400 people gathered. Officials have ordered thousands of fans to self-isolate. 

Health sources said the next 24 hours were particularly critical due to the potential infection of people at crowded venues. Carriers and contacts had also visited pubs, cafes and supermarkets.

Merlino has not ruled out further restrictions for Melbourne. “These cases are linked and that’s a good thing, but we are very concerned by the number and by the kind of exposure sites,” he said.

Of the 15 cases, six were newly reported on Wednesday. Authorities have identified 301 close contacts of the people infected and said that so far 80 have returned negative results.

The cluster has been traced back to an Indian variant of the virus found in an overseas traveller who had completed quarantine, but officials have not worked out how it spread into the wider community.

Australia’s use of swift contact tracing, local shutdowns and tough social distancing rules have helped keep its Covid-19 numbers relatively low compared with other developed countries. It has recorded just over 30,000 cases and 910 deaths since the pandemic began.

• Additional reporting by Reuters.