NSW Premier Gladys Berejiklian has made an 11th-hour decision to delay a vote in parliament on a bill that would decriminalise abortion, appearing to cave in to the concerns of Liberal colleagues.

Key points: The bill to decriminalise abortion will be debated in the NSW Upper House this week but amendments won't be considered until the next sitting

The bill to decriminalise abortion will be debated in the NSW Upper House this week but amendments won't be considered until the next sitting The earliest vote on the bill will now be mid-September

The earliest vote on the bill will now be mid-September NSW is the last state to decriminalise abortion

Debate about the bill reignited this morning as the former Minister for Women Tanya Davies described it as "a crisis of Government" and a large crowd of pro-choice protesters demonstrated on Macquarie Street.

Later, a large "choose life" sign was written in the sky over Sydney, sparking plenty of opinions on social media.

The bill will be debated in the Upper House this week, but the Premier revealed amendments will now not be considered until the next sitting.

That means the earliest a vote will take place is mid-September. It was previously going to be this week.

Ms Davies, who is now a Liberal backbencher, today escalated her criticism of the bill which she voted against in the Lower House a week ago.

"It is a crisis of Government we are facing," Ms Davies said.

"Because my community are absolutely outraged that they have been shut out and denied any opportunity to participate in this process."

Skywriting seen above Sydney CBD around lunchtime reads 'Choose Life'. ( ABC News )

In the three weeks since Independent MP Alex Greenwich announced that the bill would go before Parliament, deep divisions in the Liberal Party have been revealed.

All MPs were given a conscience vote in the Lower House and the bill passed 59 to 31 with 19 Liberal MPs voting against it.

Since then, some conservative Liberal MPs have publicly aired their grievances about the bill and the Premier's handling of the issue.

Ms Berejiklian addressed the infighting yesterday and said she had spoken to MPs about their conduct.

'Absolutely disgraceful'

As the bill heads to the Upper House for debate today, some Liberal MPs have joined with MPs from other parties and called on the Premier to step the bill aside.

Ms Davies has proposed that a committee spend up to six months drafting a new bill to decriminalise abortion.

Liberal backbencher Tanya Davies (right) with Premier Gladys Berejiklian in the background. ( ABC News )

Another Liberal, Matthew Mason-Cox, has backed the move.

The Upper House MP said the process so far had been "improper" and puts the blame at the feet of the Premier.

"The Government leadership made a decision to fast-track this bill, the fix was on from the very start to get it out of the way," he said.

"It's absolutely disgraceful.

"I have called, as many members have, for a proper process and we have been denied it time and time again."

The Shooters Fishers and Farmers Party MP Robert Borsak said threatened to stop co-operating with the Government if the bill was rushed through the Upper House.

In a statement, the NSW Pro-Choice Alliance described the decision to delay the debate as "absurd".

"The Government is ignoring the experts, [the] doctors, the women's health organisations, the lawyers and the domestic violence experts who have all endorsed this bill," Alliance chair Wendy McCarthy said.