Victoria's Deputy Premier has failed in his attempt to block the state's proposed euthanasia laws, after pulling a parliamentary move that pit him against Premier Daniel Andrews and much of his Cabinet.

James Merlino proposed a reasoned amendment to the landmark legislation which would have prevented it from proceeding.

Mr Merlino's move put him at odds with Daniel Andrews, who strongly supports the legislation and recently spoke of how his father's death pushed him to change his mind on the issue.

Mr Merlino's reasoned amendment was defeated overnight, 47 votes to 39.

Speaking this morning, Mr Merlino said while the debate was emotional, there was no animosity within the Labor Party between those with differing views.

"Yes I'm disappointed, but that's the nature of democracy and debate. There's still a long way to go," Mr Merlino said.

"I think this is a deeply flawed bill. This euthanasia legislation is a recipe for elder abuse.

"My concern is proponents of this legislation will come back some time in the future and seek to expand it."

Vote on euthanasia laws 'will be tight'

The Voluntary Assisted Dying Bill, which is currently being debated in the Lower House, is likely to be voted on tonight.

The bill's second reading was supported 49 votes to 36 overnight.

The reasoned amendment's failure and the support for the second reading indicates the bill is likely to pass the Lower House, but it will also need to pass the Upper House to become law.

Mr Merlino said he believed the vote would be close.

"I still think it's very tight and there are a lot of questions about this legislation, so I expect a pretty long debate in the Upper House as well, and a tight vote."

Under the legislation, people suffering from an advanced and incurable disease, illness or medical condition will be able to choose a doctor-assisted death from 2019.

Patients must be over the age of 18, of sound mind, expected to die within 12 months and suffering in a way that "cannot be relieved in a manner the person deems tolerable".

Doctors, relatives or friends who administer a lethal dose against the rules of a special permit could be jailed for life, under one of more than 60 safeguards the Premier claims would give Victoria the most conservative laws in the world.

Opponents argue the bill is a form of state-sanctioned suicide and there can never be enough checks and balances to ward against abuse and coercion.