Victoria has recorded five new local coronavirus cases, with locals hoping their lockdown could still be ended at midnight on Thursday.

The state is now dealing with 45 community transmission cases linked to the Melbourne outbreak, with another nine in hotel quarantine.

However, there are fears coronavirus is continuing to spread through a Melbourne aged care home after a worker tested positive over the weekend.

Arcare Aged Care Home, in the west Melbourne suburb of Maidstone, has been in lockdown since Saturday after the worker, aged in her 50s, tested positive to coronavirus late that night.

Former Labor leader Bill Shorten, whose electorate includes the aged care home, said he was hearing reports the virus had spread to partially-vaccinated residents.

"Worryingly both the staff member who recorded positive but one resident, possibly two, but one resident appears to have contracted Covid were both vaccinated in the first round," he told ABC News Breakfast.

Leading infectious diseases expert Professor Sharon Lewin said the mystery case in the aged care home was "concerning" but Melburnians should take solace in the fact that she had received the first dose of the Covid-19 vaccine.

"The mystery case is certainly concerning. [Firstly], it's a mystery case, so we need to know where this person acquired Covid. And second of all — they work in an aged care home which is the most vulnerable setting for Covid," Lewin told ABC News Breakfast.

Lewin said it was encouraging that contact tracers continued to link Victoria's new cases — but the aged care mystery case could mean lockdown is extended.

"Thousands and thousands of tests have been done, which is fantastic. And up until this one mystery case, they have all been linked which is also very reassuring," she said. "I'm very hopeful that we won't need to extend the lockdown for much longer should this sort of pattern even continue over coming days."

Arcare Aged Care Home in Maidstone was also hit by a coronavirus outbreak last year and had 14 infections linked to the home — including seven staff.

"While we hoped that this would not happen again, we are well prepared, and our infection control practices put us in a good place to manage this outbreak effectively," Arcare chief executive Colin Singh said in a statement.

Health staff were seen at the aged care home doing a deep clean over the weekend and residents were kept in their rooms.

Victoria's coronavirus testing commander Jeroen Weimar said the mystery aged care case was the state's top priority.

"It is our most vulnerable and sensitive setting that we have and that is why we have put such an important ­response into this," he told reporters yesterday.

"I am concerned that we don't have, at this point of time, an acquisition source. "This is the biggest priority for us to understand."

Victoria yesterday recorded five new local cases of Covid-19 on the third day of the state's lockdown.

Under current plans, the last day of lockdown will be Thursday, with the possibility of some restrictions extending beyond that.

New Zealand paused quarantine-free travel with Victoria amid the current outbreak, which will last until Friday, June 4, given there are no further changes.

Australian Prime Minister Scott Morrison arrived in New Zealand yesterday, and it is expected he will speak with Prime Minister Jacinda Ardern about extending the transtasman bubble beyond the two countries.

Morrison told reporters yesterday that "the idea of a bubble that goes beyond New Zealand and Australia is a real possibility".

"Fiji is going through a difficult time at the moment and we're supporting them to come through that, but whether it's Vanuatu, or the Solomon Islands or Fiji or Tonga, or any of these places, and even supporting up in Timor Leste.

"Now, these are real challenges to overcome, but when it comes to people coming to work in Australia, the seasonal workers programme ... or the broader partnership that we have across the Pacific for other purposes - this is why we get together every year."

by Natalie Wolfe, news.com.au