The Kaipara District Council is refusing to explain why chief executive Graham Sibery resigned unexpectedly after just 13 months on the job.
In a short statement, Mayor Greg Gent said Mr Sibery handed in his resignation yesterday but he would be at work next week and for "a period" after that while the council looked for his replacement.
When asked to elaborate, Mr Gent said he was not prepared to comment further.
Mr Sibery was appointed by independent commissioners to run the council and took up the position on July 4 last year.
He joined the council from a background in transportation, his past roles included director of operations and deputy rail commissioner at the Department of Planning, Transport and Infrastructure of the Government of South Australia.
Before that he worked for Veolia Transdev Australasia including two years as managing director of the business's Auckland arm, responsible for the city's passenger train network.
He replaced acting chief executive Dr Jill McPherson who was appointed after professional accountant Steve Ruru resigned in October 2014 to take up the position of chief executive of the Southland District Council.
Prior to Mr Ruru, Jack McKerchar held the position of chief executive until 2011 when he received $240,000 in severance pay because he agreed to leave his job a year before his contract ended.