Aspiring Liberal MP Michelle Loielo is pressing ahead with her challenge over the 9pm to 5am curfew which was scrapped by Premier Daniel Andrews on Sunday.

In the openings of a Supreme Court trial on Monday afternoon, her lawyers said they supported every other restriction introduced to limit the spread of the virus in Victoria.

But the curfew restriction on top of all others "is one step too far", barrister Marcus Clarke QC said.

Ms Loielo, a Mornington Peninsula cafe owner and widowed mother of three, argues the curfew infringed on her human rights.

She had initially sought an order quashing the order, but documents re-filed after the restriction was scrapped now seek a declaration that the curfew was inconsistent with Victoria's human rights charter.

Mr Clarke told Justice Tim Ginnane that the curfew was "unlawful and invalid" and "violated" Ms Loielo's human rights, including her right to liberty.

In her response, Victoria's solicitor-general Kristen Walker QC said the parties agreed that all other restrictions were necessary.

"These are extraordinary powers to be exercised in extraordinary times," she said.

Associate Professor Michelle Giles is named as the defendant in the challenge.

Ms Giles is the deputy public health commander responsible for signing off on emergency powers issued by Chief Health Officer Brett Sutton.

Ms Walker rejected claims Prof Giles had not brought an independent mind to the decision to adopt the curfew.

"The defendant ... absolutely did not act at the direction or the behest of the premier," she said.

Prof Giles is expected to be called to give evidence in the trial.

The court heard she had spent every waking hour for several days considering the restrictions and knew Victorians would die if they were not put in place, ultimately determining hardships suffered by some would be necessary to keep others safe.

In an email to Professor Sutton and his deputy Allan Cheng on September 13 she said she knew from recent experience that a significant fall in case numbers could be achieved with a curfew as part of a package of restrictions.

"Given we still have evidence of community transmission I propose that by completely removing one component we may expose the community to an unmeasured risk and the potential for an increase in cases," she wrote.

Opposition leader Michael O'Brien labelled the timing of the decision to overturn the curfew as cynical.

"Isn't it interesting that just today, as a Liberal Party member is going to the Supreme Court to challenge the legality of the curfew, the premier decided yesterday that it's not necessary any more and we're withdrawing it immediately," he told ABC Radio National.

Mr Andrews denied the decision to lift the curfew had anything to do with the legal challenge.

The trial is due to continue on Wednesday.

Australian Associated Press