Dave Evans was on holiday and driving his work's Downer ute through central Invercargill about 3pm yesterday when the acetylene gas bottle blew up.
It seriously injured his head and torso, tore the back off his ute, blew out Clyde St shop windows and threw debris up to 50 metres.
A second person was treated at the scene for shock and was later discharged.
Police were concerned other gas bottles could explode, so they evacuated the area, closed streets and set up a 200m cordon. Firefighters sprayed water on the ute for more than 30 minutes and there were no more explosions.
Locals described the huge explosion as being like a "supersonic boom." Another reported seeing a "huge fireball".
Today, Mr Evans - Downer's Invercargill workshop manager - is in a serious but stable condition in an induced coma at Kew Hospital, a Southern District Health Board spokeswoman said.
An email sent to all of Downer's New Zealand employees today from chief executive Cos Bruyn confirmed Mr Evans' accident.
"As Dave was on annual leave at the time, we cannot comment further on the circumstances relating to this event," Mr Bruyn says.
"To the extent that there are any work-related implications, a full internal investigation will be conducted.
"Downer is in support of Dave's family and we wish him a speedy recovery.
"We don't have any further comment at this stage."
New Zealand Fire Service investigators have been at the scene today trying to work out what caused the acetylene bottle to explode. Acetylene is used for welding.
WorkSafe New Zealand today confirmed that it has been informed and has officials investigating.
- By Kurt Bayer of APNZ
