An Invercargill man rushed to help after a ''huge fireball'' engulfed a man outside the shop where he worked yesterday afternoon.
''There was a massive bang, then I saw a huge fireball which turned yellow. The man came flying towards the shop and the windows of the shop [exploded] in,'' a Southern Brakes and Driveline employee, who gave his name only as Mike, said.
Emergency services raced to the industrial complex in Clyde St, just south of the central city, about 2.55pm, after an extremely loud explosion, audible throughout most of the city.
An acetylene gas bottle on the back of a utility had exploded, although it is not known yet how or why it happened. Acetylene is used for welding.
One man, aged about 40, was rushed to hospital with serious head and torso injuries and another person was treated at the scene for minor injuries.
Mike said the seriously injured man, who was driving a Downers utility, had parked outside the shop and gone inside. He was either seated in the utility or near it when the gas bottle exploded.
''I ran out there. He was badly burnt down his front. We had to cut his shirt off him.''
The explosion blew the back off the ute, as well as shattering the windows and staving in the side of a Southern Brakes ute parked beside it. Several shop windows were also shattered and debris was spread up to 50m away.
Police evacuated the area, closed streets and set up a 200m cordon, concerned other gas bottles might explode. Firefighters sprayed water on the utility for more than 30 minutes and there were no more explosions.
Employees of surrounding businesses said the explosion was huge and frightening.
''It was absolutely massive. It was like a supersonic boom,'' Annie Kennedy, from Trents Wholesale Ltd, said.
''I've never heard anything like it in my life,'' her colleague, Sue Walker, said.
Windows in their building swayed in and out, and the employees from a nearby business had told them the explosion was large enough to shake the ground, the women said.
The New Zealand Fire Service said in a statement the cordon was lifted when the area was confirmed safe by a representative from BOC gasses. An investigation into the cause of the explosion was continuing.
The Ministry of Business, Innovation and Employment had also been informed.
Less than 15 minutes after the blast, just a few blocks away, emergency services were called to a serious car crash.
Two women, a 40-year and a 20-year-old, were trapped in the car and had to be cut out before being taken to hospital with minor to moderate injuries.
