Melbourne's Covid-19 cases have surged to record levels, with officials blaming illegal home gatherings to watch a key sporting event for the spike as a hard lockdown to combat the spread of the Delta variant nears two months, reports Reuters.

Authorities in Victoria, home to Melbourne, estimate that nearly a third of 1,438 new infections could be traced back to home parties last weekend to watch the Australian Rules Football Grand Final on television.

“Many of these cases were completely avoidable ... I'm not trying to blame anyone, I'm simply trying to explain because a lot of people will be scratching their heads — how could it have gone up by so much, so fast,” state Premier Daniel Andrews said during a media briefing.

Officials admit that new cases are a “major setback” in managing the flare-up, as they race to vaccinate the state's 5.5 million adult population.