COVID-19: Confirmed Melbourne case attended Collingwood-Port Adelaide AFL match at the MCG

Football fans who attended an AFL match at the iconic Melbourne Cricket Ground (MCG) stadium over the weekend may have been exposed to COVID-19.

Four new cases of the virus were detected in the city's northern suburbs on Monday, bringing Victoria's 86-day streak without community transmission to a crashing halt. An additional five people tested positive on Tuesday, all of whom are household contacts.

On Tuesday night, Victoria's Department of Health confirmed a positive case had attended the Collingwood vs Port Adelaide AFL game at the MCG on Sunday, May 23. The case had been sitting in Zone 4, Level 1 of the Great Southern Stand.

"People seated in Zone 4, Level 1 - those with a bay between M1 and M16 on their match ticket - will be contacted directly with advice to get tested and isolate until negative," authorities said.

"Further reviews of CCTV footage will be undertaken to determine if the advice to test and isolate will be broadened beyond these areas."

Individuals who had the closest contact with the positive case will be provided with more specific advice from the Department of Health, it said.

Other attendees who were not located in the specified areas are advised to remain alert for symptoms and seek a test if any develop. 

The match was attended by 23,415 football fans, despite the AFL allowing up to 85 percent of the MCG's 100,024 capacity.

It's unclear which of the nine cases in the current cluster attended the game.

The nine infections are spread across three households. The first two, who are male relatives, were announced on Monday as "likely" cases, with urgent retesting later returning positive results. An additional two cases were confirmed later that day, both of whom are close contacts of the relatives - a woman and a preschool-aged child.

Earlier on Tuesday, a fifth case was announced. The man, who is in his 60s, was identified as a contact of the initial infection. However, it's understood the man became symptomatic before the first case.

Later on Tuesday, the department confirmed four other people had tested positive for the virus, all of whom are household contacts of the fifth case. 

Restrictions have been tightened across Greater Melbourne as a precaution. Beginning at 6pm on Tuesday (local time), masks were made mandatory in all indoor settings for people aged 12 and over. Private gatherings in the home have been capped at five visitors per day, while outdoor events are restricted to 30 people.

The AFL has already been impacted by the current outbreak, with Western Bulldogs players and staff currently awaiting test results in isolation.

A staff member at the club had visited the Highpoint Shopping Centre in Melbourne's west, where some stores are listed as Tier 1 exposure sites.