3 firefighters injured in Ashburton fire

Three firefighters have been injured fighting a blaze south of Ashburton.

Crews from across mid- and south Canterbury were called in to battle one of the biggest structural fires there in recent years.

Fifty firefighters tackled a blaze inside a 5000 square metre animal feed factory after 7pm on Monday.

"It's on the larger scale of things we deal with so we needed to call in plenty of resources from the area, we sourced them as far as Waimate and Christchurch," said Fire and Emergency New Zealand Assistant Area Commander South Canterbury Mike Johns.

Crews spent the night battling the flames that could be seen from the air.

The shed, which was used for packing and storing, contained some molasses-based animal feed, which made putting the blaze out more difficult.

"It was too hot for us to get too close to we adopted a defensive role we more or less just surrounded it to stop it spreading and try and cut it off into the back third of the building," said Mr Johns.

The three injured firefighters were taken to Ashburton Hospital.

Mr Johns says those firefighters sustained moderate burns to their lower legs, two of them remained in hospital overnight.

Sixteen hours after the fire broke out, flames are still visible amidst the ruins of the shed.

A digger was brought in to help the fire crews get full control.

"We're just going to keep dragging the iron off an expose the hotspots and stirring up the stock food in there so we can get some water on it and get it out," said Mr Johns.

What caused the blaze to break out is under investigation.