Candidates line up to replace O'Farrell

The blood had barely dried from Barry O'Farrell falling on his sword before his heir apparent Gladys Berejiklian was doing the numbers.

Within an hour of Mr O'Farrell's announcement that he was quitting as NSW Premier, the transport minister was believed to be hard at work trying to win over Liberal MPs to support her bid to replace the outgoing premier.

Ms Berejiklian, who is one of the key leaders of the party's left faction, is tipped to be the frontrunner to replace Mr O'Farrell along with Treasurer Mike Baird.

Mr O'Farrell has always seen Ms Berejiklian as his favoured candidate to succeed him.

Mr Baird is expected to win the support of the party's right faction, who have been impressed with his aggressive push to privatise the state's assets.

He is the son of Bruce Baird, who was a lower house federal MP in John Howard's government, and represents the northern beaches electorate of Manly.

Ms Berejiklian is the daughter of Armenian immigrants and holds the north shore electorate of Willoughby.

She entered the political scene as president of the Young Liberals and has gone on to become one of the better performing ministers in the O'Farrell government, managing the tough transport portfolio.

She recently launched the pay-as-you-go Opal transport card and has committed billions to the new north-west train line.

Finance Minister Andrew Constance and Community Services Minister Pru Goward are also understood to be in the running for next week's ballot.

Mr Constance may garner some support from the left and Ms Goward, who has been a particularly strong media performer on social issues, is popular among regional MPs.

Mr Baird said he was "incredibly saddened and shocked" by Mr O'Farrell's resignation but wouldn't comment on whether he'd run for the top job.