Prime Minister John Key has described his former Northland colleague Mike Sabin as potentially having the makings of a Cabinet minister.
Mr Sabin announced on Friday that he had resigned from Parliament, effective immediately, because of "personal issues" that were best dealt with outside Parliament. He has made no further comment.
Mr Key said the party had not asked for his resignation.
"Up until his resignation I've had enormous confidence in him as an MP," he added.
"Actually I think he has performed very strongly. He's got a great grasp of some of the policy area. I actually saw him as someone that would be potentially a future Cabinet minister if we were in government."
He had been aware that Mr Sabin, who had been a good, hard-working local MP, had been planning to resign one or two days before he did so, and had become aware of the issues he had referred to in about the last week of the parliamentary term last year.
"He made a very significant contribution to our caucus. He's a loss in terms of the contribution I've seen him make as a politician," he said.
National Party president Peter Goodfellow also acknowledged Mr Sabin's service his constituents and the party since his election in 2011, while former Northland electorate chairwoman Sally Macauley said his resignation was extremely disappointing for the party, but she understood his decision, and was looking forward to a new candidate who would again support Northland and its people.
"I've known Mike for more than eight years, initially through the good work he did to eradicate methamphetamine from the community," she said.
"He was totally dedicated to enhancing Northland's economic development and attracting industry to the region.
"It's a demanding job, not only involving long days in Parliament but also the need to listen to constituents.
"This is a very hard time for Mike, and we must respect his privacy," she added. She did not believe Mr Sabin's resignation would affect support for the party or its new candidate.
Meanwhile Mr Sabin's main rival in last year's election, Labour candidate Willow-Jean Prime, is keen to contest the seat again, despite having become a mother for the first time last week. The lawyer and current Far North District councillor, who lives near Moerewa, said she had already contacted the party's general secretary, Tim Barnett, to say she wanted to stand in the by-election.
Last year she won 8969 electorate votes to Mr Sabin's 18,269, reducing his 2011 majority by more than 2000 votes.
Mr Sabin won the candidacy for one of the safest seats in the country in 2011 following John Carter's retirement after 24 years. Also shortlisted were YWCA manager Sarah Davies (Taheke), farmer, businessman and former detective Matt King (Okaihau), company director Ken Rintoul (Okaihau) and Kaitaia school teacher (now principal) Mark Tan.
The other early contenders included Maryanne Baker (Paihia), Victor Cauty (Kerikeri), Mita Harris (Puketi), Wayne Linton (Maungaturoto), Roger Ludbrook (Ohaeawai), Grant McCallum (Maungaturoto), Di Maxwell (Waipapa) and Jeanette Richardson (Opua).