A week after visiting his dying grandmother in hospital, Premier Dominic Perrottet stood in NSW parliament to oppose laws that would allow her to end her suffering sooner.

The parliament is debating a bill that would give terminally ill people in the state access to voluntary assisted dying.

Speaking on Friday, Mr Perrottet said the issue was something “very real and personal” to him.

His grandmother, aged in her 90s, is dying of pancreatic cancer.

“I sat next to her holding, her hand. I could tell that she was in great pain and that she wanted it to be over.

“I got a sense, as much as anyone can have, why those in such pain would want to end it quickly. So this debate is not abstract for me”.

But Mr Perottett said the proposed laws mark a “threshold moment”.

While the bill restricts euthanasia to terminally ill people who would die in no more than 12 months, if it passed, Mr Perrottet said it would open the door for euthanasia to be allowed in other circumstances.

“This debate is fundamentally about how we treat that precious thing called human life,” he said.

“If we crossed crossed this threshold, this parliament should be under no illusions as to what it would do.”

He cited countries such as Canada, Belgium and the Netherlands, which also originally legislated for terminally ill people.

• Related: Queensland Parliament passes voluntary assisted dying bill

But now people with psychiatric disorders, dementia sufferers, and newborns with a disability were some of the cohorts for which euthanasia was approved, he said.

Instead of passing voluntary assisted dying laws, NSW should improve the quality of its palliative care, Mr Perrottet argued.

“I failed in my former capacity as treasurer to address this issue but as premier, I will fix it.”

While Mr Perrottet will vote no, members of his Liberal Party have been afforded a conscience vote on the issue.

Opposition Leader Chris Minns has also said he will vote against the reform, but Labor MPs will also be able to vote their conscience.

NSW is the only state that is yet to pass voluntary assisted dying laws.

The bill was tabled in parliament last month by Sydney MP Alex Greenwich, with a record 28 co-sponsors from across the political spectrum.

Opponents have also shared concerns people could be coerced into taking their lives through euthanasia, or that people may be able to game the system.

Summer Hill MP Jo Haylen, one of the bill’s co-sponsors, said on Friday that the legislation was packed with strict safeguards.

Two independent doctors will have to assess applicants, and the bill makes attempting to place duress on or induce a person to apply for voluntary assisted dying a criminal offence.

“This is a compassionate bill. It is a considered bill,” Ms Haylen said.

Palliative care is important but it cannot manage the pain of many terminally ill people, she said, citing stories from her constituents.

One told Ms Haylen her terminally ill aunt, who was essentially slowly starving to death, was forced to take her life in secrecy in the absence of voluntary assisted dying laws.

Another wrote to Ms Haylen about the impact watching the terminally ill suffer has on their family.

“The memory of my mother’s last days alive will always ignite feelings of anger, desperation and trauma that my mother could not pass away in peace,” Natasha from Ashfield wrote.

“I strongly believe that no other terminally ill people or their family should experience what we endured. It is inhumane.”

Debate will continue into 2022, after the government and Labor agreed to refer it to an upper house inquiry which is due to report back on the first sitting day next year.

-AAP