This recurring tagline is telling evidence that Victoria's Parliament is not voting on whether or not to help terminally ill people die a quicker and less agonising death, Deputy Premier James Merlino said.

Rather, they are being asked to vote to legalise suicide, and to "forever change the doctor-patient relationship".

"The irony that articles on assisted dying in our papers are almost always footnoted with a reference to a suicide prevention hotline should be lost on no one in this house," Mr Merlino said.

"It is a small and awkward admission that suicide is exactly what is being countenanced here."

Mr Merlino, a devout Catholic, is the most senior member of the Andrews government to have declared his opposition to the legalisation of voluntary assisted dying in Victoria.

On the first day of what will be a marathon debate on the issue this week, in which all 127 MPs will have a chance to speak, he sought to block the bill's passage and introduce an amendment to resolve five concerns about its argued flaws.

This includes poor access to palliative care for low income and rural people, uncertainty about what substance would be administered, the risk of "doctor shopping and assisted death clinics", a lack of protection against family violence and elder abuse, and a lack of safeguards for the disabled.

"If this law needs 68 protections to keep our citizens safe, how risky is this proposition? That's 68 things that can go wrong," Mr Merlino said.

Earlier, Premier Daniel Andrews spoke of those who were taking their own lives now because the state does not sanction euthanasia, in an emotionally charged speech observed by his wife Catherine Andrews in the gallery.

A coroner's report found that already in Victoria about 50 terminally ill people a year were dying by suicide "quietly and violently in our suburbs and towns", Mr Andrews said.

"Speaker, I am not prepared to read aloud some of the methods that people have used. I'll just leave you to imagine your greatest fear, because it's probably on the list."

Mr Andrews famously changed his position on assisted dying after experiencing his father's death from cancer, and he spoke again of his father's final days in hospital - what he called "a good death".

"No one should have to suffer a bad death in the name of good ethics," he said.

The vote is not binding along party lines, with the exception of the Greens who have a policy position in favour of assisted dying.

MPs who spoke on Tuesday were guided by their conscience in a debate that lived up to the hope that the issue would bring out the best in the Parliament.

Those who said they would vote yes included Labor ministers Tim Pallas and Martin Foley, and Liberal backbenchers Roma Britnell and Brian Paynter.

Ms Britnell, who was a nurse for 30 years before she replaced former premier Denis Napthine as the MP for South-West Victoria, said she was moved to vote yes by the distress of nursing many patients to a slow and agonising death.

"I will never know whether any of the people I nursed would have chosen the pathway that this legislation would offer them, but I do know that many of them could have felt some comfort knowing that was available to them," Ms Britnell said.

Those who declared they would say no include Labor minister Marlene Kairouz, Labor backbencher Lizzie Blandthorn, Nationals leader Peter Walsh, shadow attorney-general Robert Clark and Liberal backbenchers Graham Watt and Michael Gidley.

One MP, the Nationals' Emma Kealy, told Parliament she was still undecided, but expressed serious reservations due to the failure to settle on what the lethal medicine would be.

Her Nationals colleague, Peter Crisp, said he would vote for Mr Merlino's amendment, or in other words, vote no.

Mr Andrews said earlier in the day that he would not accept any amendments to the bill.

"We've got this model right," he said.

The first day of debate was expected to conclude at roughly 1am after a 12-hour session.

A vote is expected on Thursday or Friday.

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