NSW is the only state in Australia that does not allow assisted dying for terminally ill people.

The state's upper house passed legislation at the second reading stage in a 20 to 17 vote on Wednesday night.

Upper house MPs will debate amendments to the bill next Wednesday, with a final vote due after that, Independent MP for Sydney Alex Greenwich said.

The landmark legislation passed the lower house with a majority of 20 last year.

"This has been a long journey, a long and overdue journey," Mr Greenwich said.

"We know that NSW is the last state to embrace this compassionate reform."

Mr Greenwich said the bill is one of the most conservative models on the issue in the country, with 46 amendments already passed.

"It's my call to the upper house to not create any barriers and let's work to seek to achieve voluntary assisted dying in NSW by the end of next week," he said.

The Voluntary Assisted Dying Bill was introduced to the parliament with 28 co-sponsors, more than any other piece of legislation in Australian history.

Supporters of the bill rallied outside NSW parliament on Wednesday.

"We have waited a long time, as in 50 years Dying With Dignity has been campaigning for these laws," Shayne Higson, president of the NSW branch told AAP.

"We have to keep the pressure up because we know that the legislation is not supported by our premier.

"Fortunately, there are enough MPs in NSW parliament who reflect the support in their communities and now that support is also being shown in the upper house."

The Catholic Archbishop of Sydney Anthony Fisher said the "kill bill" divided society into two classes of people - those whose lives were protected by the state and those whose deaths were facilitated because their lives were deemed to be "not worth living".

"I fear, that this bill will dehumanise the medical and nursing professions, creating a health industry where it might become more cost effective, or expedient, to push people towards death," he said in a statement.

Australian Associated Press