Two firefighters have been treated by ambulance at the scene of a fire at a Napier fertiliser plant after getting sulphur dioxide gas in their eyes.
Hawke's Bay fire area commander Kenneth Cooper said the gas irritated their eyes but did not cause damage.
"During the course of firefighting they threw copious amounts of water on the sulphur, which creates a sulphur dioxide gas which is an irritant," he said.
The firefighters were treated with eye washes and are now back on the job, he said.
Mr Cooper said the fire had now been put out but 20 firefighters remained at the scene for decontamination of their gear which had been exposed to sulphur dioxide gas.
He said SH2 is expected to reopen but emergency services were still asking drivers to take alternate routes.
"There is quite significant congestion in that area so if the public could avoid it that would be great," he said.
Hawke's Bay District Health Board is urging people downwind of the plant to stay inside, close windows and doors and turn off air-conditioning units to stop dangerous fumes entering their homes.
Medical Officer of Health Nick Jones said people, especially those with breathing difficulties like asthma or bronchitis, could be affected by the smoke coming off the burning sulphur.
When sulphur is burnt it releases the toxic gas sulfur dioxide, which can have a suffocating effect.
If the gas mixes with water molecules it can produce acid rain.
A storage shed containing around 1000 tonnes of sulphur has caught fire at a fertiliser plant in Napier this afternoon.
The fire has caused police to close SH2 between Hastings and Napier because of fears about hazardous fumes from the burning sulphur.
Fire communications shift manager Mike Wanoa said when fire crews arrived to the scene they found a large fire in the five-storey storage shed.
Mr Wanoa said the fire was located in the roof area, conveyor belt and the sulphur pile in the storage shed.
Ravensdown chief executive Greg Campbell said the fire has been contained but fire crews were expected to remain onsite until 8pm.
Ravensdown fertiliser plant in Napier
"Most importantly our staff are safe and well and have all been sent home excluding essential personal," he said.
"We are aware this has impacted on our neighbours and we appreciate their understanding and will be in touch with further information as soon as we can."