The Fire Service is facing the difficult process of removing gas cylinders from a burnt out truck in Nelson.
The truck carrying about 60 cylinders of gas caught fire about 6.40am on Quarantine Rd.
An evacuation zone of 500m around the truck was set up and the road was closed.
Nelson Fire Service station officer Craig Davies said the truck driver found his rear trailer on fire, pulled over and called 111.
The fire was now extinguished, but the road remains closed while the Fire Service deals with the gas cylinders.
Assistant area commander Des Irving said it was difficult as some of the cylinders have popped and heated up.
Firefighters were confident the cylinders had cooled down but they would have water jets on stand-by just in case.
The scene will then be passed over to police to investigate.
Nelson police said residents in the area were asked to stay indoors, particularly those downwind of the fire in the Parkers Rd direction.
Police asked the public to stay away from the area.
At this stage it was not known what had caused the fire.
Gym-goers were evacuated from City Fitness about 6.40am, with some reporting that they heard a "boom, boom" before people came in saying there was a fire.
The truck is thought to be a Summerland truck which had just arrived in Nelson from Christchurch carrying cylinders of oxygen, nitrous oxide and acetylene.
- Additional reporting: Nelson Live