Victorian Premier Daniel Andrews says the state government is negotiating with crossbenchers over the controversial COVID-19 Omnibus bill.

The Victorian government is negotiating with crossbenchers over its controversial COVID-19 Omnibus bill.

Prominent legal figures have written an open letter, saying some provisions in the bill are "unprecedented, excessive and open to abuse".

Reason Party MP Fiona Patten also will not vote for the bill unless there are amendments.

The government needed cross-bench support earlier this month to extend its emergency powers by six months, after initially wanting a 12-month extension.

"We'll have a good-faith negotiation process with the cross bench as we do on all issues," Premier Daniel Andrews said on Wednesday.

"We saw the results of that when we last went to the parliament with a COVID-related matter.

"Those discussions continue. I don't have an update on where they're at, but our normal practice is to engage meaningfully and in a good-faith way."

The 14 retired judges and QCs said they were "deeply concerned" that the bill went through state parliament's lower house last week.

The bill is due to go before the upper house next month.

There are growing concerns about a section of the bill that gives more powers to authorised officers to detain people, as part of the state government's coronavirus restrictions.

But Mr Andrews again defended the bill on Wednesday, saying there would be sufficient oversight.

"The key point here is that there are structures and oversight and accountabilities, there's a formality to this and, again, the debate can be had on the floor of the parliament," he said.

Ms Patten said she would not vote for the bill in its current form and would probably want it voted on clause by clause.

Mental Health Minister Martin Foley said the detention powers in the bill could be applied to people who have mental health issues.

"You have to deal with the reality that this is a wildly infectious virus," he said.

"A very, very small number of people who may be exposed to it (the virus), in limited circumstances sometimes need - short of compulsory detention for mental health issues, but for their public health wellbeing for themselves and the wider community - those are the kinds of circumstances envisaged for the omnibus bill," he said.