The district health board chief executive being investigated for unexplained spending has resigned.

Dr Nigel Murray has resigned from Waikato District Health Board with immediate effect, a statement from the board said today.

"An independent inquiry has identified that Dr Murray had spent more than the agreed $25,000 allocated for relocation costs, and other unauthorised expenses involving potential financial breaches of the chief executive's obligations," the statement said.

The board has accepted Murray's resignation with immediate effect, on the basis that he repay all outstanding amounts.

"The board acknowledges that this has been a challenging time for Waikato DHB staff and the Waikato community."

The board is to now commence a search as soon as possible for a new chief executive.

Murray has been on leave from the $560,000 a year job since July 22 when the investigation was launched.

An Audit New Zealand review of the processes and management of the expenses including authorisation and payment of the money was also conducted.

Murray came under fire from government watchdog the State Services Commission in December for not disclosing his yearly expenses for his first two financial years in the role.

When they were disclosed in January the Herald revealed he had spent $108,000 of taxpayer money on international and domestic travel for work.

That included $36,000 of relocation costs from Canada to Hamilton and $11,700 for early arrival accommodation costs after Murray left his job at Fraser Health in British Columbia sooner than expected.

Nigel Murray at a glance

• July 2014: Nigel Murray hired by Waikato DHB chairman Bob Simcock as chief executive despite Simcock being warned by several parties against the appointment.

• August 2014: A Canadian Government review of Fraser Health shows the authority to be one of the worst performing in the country.

• March 2015: Was a no-show at a conference and delegate site visit in the US he was invited to. Said he was conducting other business.

• December 2016: Under fire from the State Services Commission for not disclosing annual expenses for two financial years.

• January 2017: Expenses show he spent $108,000 of taxpayer money travelling internationally and domestically for work.

• June 2017: Minister of Health Jonathan Coleman informed of concerns raised about Murray's expenses. Waikato DHB board members left in dark for five weeks.

• July 2017: Murray goes on annual leave for two weeks while Waikato DHB launches investigation.

• August 2017: Midlands Health Network, representing 400 GPs, writes to Ministry of Health director-general Chai Chuah complaining that Murray is difficult to work with.

• August 2017: Murray extends his leave as investigation not completed within initial three-week timeframe.

• September 2017: Investigation completed and reported to remuneration committee of the board.

• October 2017: Murray resigns from CEO position.