Cordons for residents living around the site of a large sulphur blaze at a Hawke's Bay fertiliser plant have been lifted and State Highway 2 has been reopened.
Area commander Ken Cooper said all residents are allowed back to their homes, including those directly across from the factory.
He said there was now no risk to the public, with the fire fully put out and air monitoring stations set up, which showed there were no persisting traces of sulphur dioxide in the air.
Homes were evacuated earlier on Thursday as about 60 firefighters battled the blaze.
The fire broke out in a five-storey-high sulphur shed at the Ravensdown plant between State Highway 2 and Waitangi Rd at Awatoto, south of Napier, about 2.45pm.
Crews from across the region were called in to fight the blaze in the shed containing about 800 tonnes of sulphur.
Hawke's Bay area commander Ken Cooper said two firefighters had been treated at the scene.
"To fight the fire we've had to put quite large quantities of water onto the sulphur and that's produced sulphur dioxide gas, which is an irritant. A couple of firefighters got some of the irritant in their eyes. It's quite a simple case of washing that out in an ambulance at the scene."
Cooper said State Highway 2 would be opened again before 7.30pm.
"Traffic is backed up almost back to Hastings, there's pretty serious congestion in that area. People have been in the traffic for about an hour now."
He said police had diversions in place and roads would likely be cleared in an hour's time.
The fire was still causing disruption on roads, with traffic moving very slowly on Farndon Rd, State Highway 2 between Napier and Hastings and Pakowhai Rd, police said.
People were being asked to consider delaying driving home or finding an alternate route, such as via Taradale or Fernhill.
Properties in the area were evacuated as potentially dangerous sulphur dust – which can combust at relatively low temperatures – and other hazardous material was blowing from the plant.
Health officials were urging people living near Awatoto or downwind of the Ravensdown Factory to stay inside with windows and doors shut and to turn off air-conditioning units.
Medical officer of health Nick Jones said smoke from the fire and the burning sulphur could affect people who had breathing issues like asthma or bronchitis and make their conditions worse.
Anyone experiencing breathing difficulties should get medical help, Dr Jones said.
Anyone travelling between the two cities was advised to use the Napier-Hastings expressway rather than the SH2 route.
Earlier, Fire Service assistant area commander Nigel Hall said 60 fire fighters were at the scene and he expected it would be a "long, drawn out" incident.
"We have got a smouldering fire in the second shed. In there we have got about 800 tones of sulfur which is particularly nasty," he said.
"We have been inside the building firefighting working with low pressure deliveries. There is a possibility of dust explosions with this particular product so the people working inside are only using spray instead of jets."
Hall was unsure how the fire started but believed it began on the conveyer belt which runs across the top of the sulphur shed.