Police were called to the fire in the suburb of Kelvin Heights at 9.30pm on Tuesday.
Southern Fire Communications spokeswoman Lyn Crosson said a specialist fire investigator went back to the wreckage yesterday morning to work out what caused the car to burst into flames.
Lindsay Shaw, whose house looked out across the park, told Radio New Zealand her "whole house shook" when the car went up in flames.
"It was just a horrendous explosion . . . we could see that there was a vehicle engulfed in flames, like it was instant." A photographer at the scene said the entire suburb of Kelvin Heights was blocked off by armed police.
He could not get within 5km of Jardine Park. A tour bus and about 20 cars were among those stopped by the cordon.
An Otago Daily Times reporter in Queenstown said a cordon had been set up at the intersection of State Highway 6 and Peninsula Rd, about 7km from Jardine Park.
A witness could see the exploded vehicle in the middle of a large field and said it had been destroyed.
A photo from the scene shows a burned-out vehicle, with its hood up and emergency services nearby. The vehicle appears to be a station wagon.
Yesterday, Sturgess' father told the Herald "it was a sad business all around".
Sturgess left home in the morning and his family put out a missing person's message on Facebook through a friend later in the day after failing to get hold of him, he said.
"It was out of character and it just happened and it went from bad to worse."
Sturgess' mother told Fairfax the news was "a bolt out of the blue".
"His wife is pretty cut up of course and his little son is asking where 'Dada' is. His father and myself are pretty shattered."