At a press conference this afternoon Ms Berejiklian said standing aside from the office of premier was not an option, so she had no choice but to quit.

Ms Berejiklian said that after setting a rule that any minister in her government must step aside if under investigation by ICAC, the rule must apply to her too.

But she could not stand aside when the final ICAC findings may more more than a year away.

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Ms Berejiklian said history would show she did nothing wrong.

"It pains me to announce that I have no option but to resign from the office of premier," she said.

"I have always acted with the highest level of integrity.

"My resignation as premier could not occur at a worse time," she said. "But the timimg is completely outside of my control as the ICAC has chosen to take this action during the most challenging weeks, of the most challenging times of this state's history.

"Resigning at this time is against every instinct of my being and is something I do not want to do.

"I love my job and I love serving my community. But I have been given no option to continue as premier would disrupt the state government at a time when our entire attention should be focused on the challenges confronting NSW.

"I have absolutely no regrets during my time in public life."

Ms Berejiklian said her resignation would take effect once the NSW Liberals chose a new leader. She will leave parliament once a byelection for her northern Sydney seat of Willoughby can be arranged.

After her statement Ms Berejiklian left without taking questions.

"Do you regret not reporting Daryl Maguire earlier, Premier?" one journalist asked but Ms Berejiklian continued out the door.

ICAC said in a statement earlier today that it is investigating whether Ms Berejiklian engaged in conduct that "involved a breach of public trust" during her secret relationship with former MP Daryl Maguire.

ICAC will hold a public hearing on October 18 under Operation Keppel, which is investigating whether Ms Berejiklian engaged in misconduct in connection with grant funding to the Australian Clay Target Association, or the Riverina Conservatorium of Music, in Wagga Wagga.

ICAC also said it was investigating whether Ms Berejiklian's conduct involved the "dishonest" exercise of her official duties by not reporting concerns over potential corrupt conduct by Mr Maguire, the former member for Wagga Wagga, who advocated for the grants.

In 2020 the Premier admitted at an ICAC hearing that she had been in a secret relationship with Mr Maguire for five years.

Ms Berejiklian has on several occasions been asked at press conferences in the past month whether she is a person of interest in the ICAC investigation but has not confirmed it.

She has also been asked whether she should step aside if she were under investigation, but has avoided answering.

Mr Maguire resigned under a cloud in 2018 after admitting to ICAC that he sought payment for a property deal.

Operation Keppel is also investigating whether Mr Maguire misused his office by obtaining benefit for himself.

More of this story to come ...

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