Ms Berejiklian appeared before the Independent Commission Against Corruption on Monday morning as part of its investigations into Mr Maguire.'s business dealings during his time in parliament.

She admitted to a "close personal relationship" with the former MP and said the pair had continued to communicate until less than a month ago.

The revelation prompted a furious reaction from opposition leader Jodi McKay who called for Ms Berejiklian to resign or face a vote of no confidence in parliament on Tuesday.

"If you thought you knew Gladys Berejiklian, think again," Ms McKay told reporters.

"This premier is a fraud and today she has been unmasked."

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But when fronting her own media conference this afternoon, Ms Berejiklian admitted she had made mistakes in her personal life but said she had done nothing wrong and would not stand down as premier.

She said she had remained in contact with Mr Maguire until recently because she did not believe she could abandon a friend going through a difficult time.

"Hands down this has been one of the most difficult days of my life. I am an extremely private person and, without question, I stuffed up my personal life," Ms Berejiklian said.

"It's very difficult for someone in my position to have a private and personal life and I'm very upset at what has transpired but I want to make this assurance to the people of NSW: I have always put the public first.

"I have always made sure that public interest is first and foremost paramount in every single thing that I do ... The role I have is the greatest privilege of my life and while I have made this mistake in my personal life I intend to serve the people of NSW to the best of my ability."

Ms Berejiklian said she had trusted Mr Maguire and felt let down by him.

"Had I known then what I know now, clearly I would not have made those personal decisions," she said.