A powder silo at the Fonterra plant in Edendale has exploded and collapsed on itself, a fire service spokesman says. A source said the explosion happened in the D4 silo and a small part of a building has collapsed, rupturing some pipes, including a steam pipe, on the way. The collapse also tore open a milk silo with a capacity of 250,000 litres, leaking milk across the site. A Fonterra spokeswoman confirmed the collapse, and said all staff were accounted for. She was not sure whether operations at the plant had ceased, or what other areas of the plant could have been affected. The fire service spokesman said about six fire trucks were either on the way or already at the scene, with teams from Kingswell, Invercargill, Mataura, Gore, Wyndham, and Edendale responding to the incident. The fire command unit has arrived on site and it's understood the factory is now in lockdown. A St John Ambulance spokesman said there was one ambulance and one first response unit at the scene, but there appeared to be no people needing treatment. A police spokeswoman said traffic diversions were expected to be put in place at Coalpit Rd and Homestead Rd. An eye witness said steam appeared to be coming from part of the plant and it looked as though something had collapsed. What appeared to be a "geyser of steam" was coming out of part of the plant, the witness said. The geyser has since died down. Tankers were still entering the site and it is understood Fonterra staff have been instructed not to speak. An Environment Southland spokesman said staff were on their way to the scene from Invercargill about 3pm. They would check whether there were any potential spills which could contaminate waterways, however there had been no reports as such, he said. The Edendale plant has been operating for more than 133 years and is the country's oldest manufacturing site, Fonterra's website says.