Invercargill mayor Tim Shadbolt is recovering in hospital with chest and back injuries after the car he was driving rolled onto its roof near Winton, in Southland.
Police have launched an investigation into the crash which happened about 9pm on Friday on a bend of State Highway 6 about 1km south
of Winton.
Police area commander Inspector Barry Taylor said it was too early to speculate on the cause of the accident.
"I anticipate that the enquiry will take some four to six weeks."
Mr Shadbolt was one of three males in the car.
Winton St John ambulance station manager Shane Batchelor said two men were taken to Kew Hospital in Invercargill with moderate injuries.
Mr Shadbolt was treated at the scene for spinal injuries and he is understood to have fractured several vertebrae.
Mr Batchelor told NZPA it had been a "lovely evening" at the time of the crash and no other vehicles were involved.
Mr Shadbolt was returning from Queenstown -- where he had been on mayoral business -- in the mayoral car.
Invercargill City Council chief executive officer Richard King said doctors were still assessing Mr Shadbolt's condition and he was not receiving visitors.
Mr King asked for well-wishers and the news media to respect the wishes of Mr Shadbolt's family for privacy.
"Tim is extremely popular all over New Zealand and is usually the first to front up to the media and the public, but right now he needs to recover and we ask people to give him some space."
Southland District Health Board communications manager Megan Grindlay said Mr Shadbolt was in a satisfactory condition at Southland Hospital and was making good progress.
In line with the wishes of Mr Shadbolt and his family the hospital would not be releasing any further details, she said.
Mr Shadbolt was first elected mayor of Invercargill in 1993 but was defeated in 1995 but remained on the council.
He was re-elected to the mayoralty 1998 and has been the mayor -- in his fourth term now -- ever since.
In 2001 he was re-elected unopposed and in 2004 he won with a huge majority.
Mr King said that while Mr Shadbolt was recovering, deputy mayor Neil Boniface would be acting mayor.
- NZPA
