The first minister has fallen from the recently elected NSW Labor government following misconduct allegations relating to an undeclared family property interest.

Premier Chris Minns announced in a snap briefing on Wednesday that he had asked Skills Minister Tim Crakanthorp to resign from his various portfolios over a failure to disclose conflicts of interest.

Mr Crakanthorp agreed to quit his roles, including as minister for the Hunter.

The Newcastle MP did not until recently declare significant commercial land holdings owned by his wife and her parents in the Hunter region, constituting a significant breach of the ministerial code of conduct, the premier said.

After learning of the potential conflict on Wednesday, Mr Minns said he lost confidence in Mr Crakanthorp.

“This has given rise to concerns that he may have acted in matters in which he had conflicts between his public duties and his private interests,” the Premier told reporters at a snap press conference.

The matter has been referred to the NSW Independent Commission Against Corruption.

“If they open an inquiry and regard it as serious enough to launch an investigation, no, he cannot stay in the NSW parliamentary Labor Party,” Mr Minns said.

Mr Crakanthorp’s rationale for not declaring the interest to the Cabinet Office remains unknown.

“He can communicate that to you and the Independent Commission Against Corruption,” Mr Minns said.

Mr Crakanthorp has been contacted for comment.

Deputy Premier and Education Minister Prue Car will take the skills, TAFE and tertiary education and training portfolios on an interim basis.

Police Minister and Swansea MP Yasmin Catley will assume responsibility for the Hunter.

The resignation prompted the opposition to call for Mr Minns to answer questions asked in recent months about other perceived conflicts of interest in his cabinet.

“The government has shown a blatant disregard in parliament to questions regarding a number of perceived conflicts of interest of other ministers,” a Coalition spokesman said.

Mr Crakanthorp’s family’s property interests also hit the spotlight during his successful byelection campaign in 2014.

The land holding had been declared to the Newcastle City Council, where Mr Crakanthorp was a local councillor.

The ministerial code of conduct states it is essential for public confidence that ministers pursue and be seen to pursue the best interests of the people of NSW to the exclusion of any other interest.

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

The anti-corruption commission in June 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.

-AAP