A Melbourne man who tested positive to COVID-19 after attending the cricket at the MCG and Boxing Day sales at Victoria’s biggest shopping centre has sparked an emergency as authorities race to discover who he caught the virus from.

The mystery case was the only one outside of hotel quarantine in Victoria on Wednesday, and has prompted a scramble to identify its source for fear it could be linked to many others yet to be diagnosed.

The man, aged in his 30s, attended the second day of the Boxing Day Test at the MCG on December 27, where up to 30,000 spectators were at the ground.