A chemical spill closed streets and caused hundreds of people to be evacuated as central Dunedin ground to a halt yesterday.
Traffic was severely backed-up on the one-way street system after an ammonia leak at Cadbury's Dunedin factory triggered the evacuation of Cadbury's and surrounding businesses' premises.
Emergency services were alerted to the leak after an automatic alarm activated at 1.17pm.
Four fire appliances, a ladder truck and a command unit attended the incident and two firefighters in hazmat suits entered the factory with a Cadbury's engineer to isolate the leak.
Fire Service Senior Station Officer Jason Hill, of Dunedin Central, said the ''significant'' leak led to the evacuation of Cadbury's central city facilities and nearby businesses in Castle and Cumberland Sts as small amounts of the gas leaked into the one-way street system.
Both streets were closed from St Andrew St to Stuart St and Anzac Ave was also closed, causing traffic to back-up for several blocks, delaying motorists and causing detours.
It was unclear how much ammonia leaked as a result of a mechanical failure at the factory but a cloud of the gas was ''quite noticeable in the courtyard of the building'', Mr Hill said.
St John paramedics assessed an engineer who had been close to the leak, but no-one was injured, he said.
The ammonia had provided an additional challenge for firefighters.
''It attracts itself to moisture ... it can cause skin irritation and you don't want to be breathing in ammonia at all,'' Mr Hill said.
After firefighters had isolated the leak, they used fans to ventilate the factory.
About 200 evacuated Cadbury workers had to wait for more than two hours before returning to work.
All roads were reopened by about 4pm.
Cadbury's parent company, Mondelez, said the cause of the leak was under investigation.
Ammonia was used as a cleaning agent within the factory, Mondelez Australia and New Zealand head of corporate and government affairs Celin Huseby said.
''We can confirm that all employees were immediately evacuated, and that all are safe and uninjured,'' she said.
''We are in the process of conducting an internal investigating to ascertain the cause of the leak.''
There were unconfirmed reports an explosion at the plant caused the leak, but Mondelez could not confirm that.
Firefighters told businesses in Castle and Cumberland Sts to evacuate workers just before 2pm.
''They said it was a major ammonia leak and just to get out,'' a worker evacuated from a nearby Castle St business said.
Two tour parties in the Cadbury's factory were evacuated, it is understood.
Tali Paz, of Israel, was a member of one of the tours.
''We were inside the purple silo, the big one, and we were supposed to have the chocolate fountain come down and then the fire alarm came on and the tour guide took us straight downstairs.
''We saw the smoke come from inside the building and there was a smell - a strong smell,'' she said.
Everyone was calm and there was no danger, she said.
The Cadbury night shift went ahead as normal.