Questions remain after NSW Premier Chris Minns prompted the resignation of one of his ministers and referred him to the state’s corruption watchdog.

Newcastle MP Tim Crakanthorp will move to the back bench and his future in the NSW Labor Party is under a cloud after he failed to declare property holdings while minister for the Hunter region.

Mr Minns said he learned earlier this week Mr Crakanthorp’s wife and her parents owned a significant number of commercial real estate properties in the Hunter.

That triggered an order for Mr Crakanthorp, who had been a minister in the four-month-old NSW Labor government, to formally detail all known private holdings held by family members.

After reporting those holdings and a potential breach of the ministerial code of conduct on Wednesday, Mr Crakanthorp resigned and was referred by Mr Minss to the ICAC.

Mr Minns declined to reveal how he first learned of the property interests.

“That will be a matter to be investigated by the Independent Commission Against Corruption,” he said at a snap media conference on Wednesday.

“I’m not trying to be coy or have intrigue in relation to those matters but it’s important that they’re able to do that free of commentary from the government.

“If they communicate with us about their determination, I’ll make that public.”

Mr Crakanthorp’s rationale for not declaring the interest to the Cabinet Office and how it learned of the conflict, remains unknown.

In a late night speech to parliament, Mr Crakanthorp said he had previously disclosed two properties his wife had an interest in but unfortunately omitted a third.

When notifying about the third, he also disclosed his father-in-law owned property at Broadmeadow, a Newcastle suburb.

He said he later became aware properties owned by his in-laws within Broadmeadow also now represented a conflict of interest.

Discussions in recent days with his wife’s parents and siblings resulted in “a full list of each of their interests” being provided to the Premier’s Office, Mr Crakanthorp said.

“I appreciate and firmly believe ministers must be held to the highest standards and would like to note that this oversight was identified due to my own self-reporting,” he said.

Mr Minns said he had concerns Mr Crakanthorp “may have” acted in matters where he had conflicts between his public duties and his private interests.

Should ICAC launch an investigation, the former minister will be booted from the parliamentary Labor Party, Mr Minns said.

Opposition Leader Mark Speakman said Mr Minns must further detail the commercial real estate holdings, ministerial decisions potentially impacted by them and the future of those decisions.

“What we’ve seen in the first 129 days of this government through inexperience [and] arrogance is a failure to manage conflicts of interest properly,” he said.

Breaches of the ministerial code, on their own, can be means for a finding of corrupt conduct by ICAC.

In June, the NSW anti-corruption commission found former premier Gladys Berejiklian had engaged in serious corrupt conduct by involving herself in decisions in Wagga while in a long-term romantic relationship with Wagga MP Daryl Maguire.

As a result of Mr Crakanthorp’s resignation, Deputy Premier Prue Car will take the skills, TAFE and tertiary education and training portfolios. Swansea MP Yasmin Catley will add the Hunter to her police and counter-terrorism portfolios.

– AAP