Five crews were called to the blaze at the Ring Road factory, about 5pm yesterday.

More than 20 firefighters took just over an hour to bring the fire under control.

Fire authorities believe a power failure caused the fire in one of the crinkle cut deep fryers after a conveyer belt failed, allowing chips to sit in fat longer than normal.

Flames soon spread into the extraction unit and roof.

Country Fire Authority duty officer Gavin Hope said the fire was almost three storeys high when crews arrived.

"McCains has a false ceiling which was hard to access, so it took a bit of time to actually reach the fire," Mr Hope said.

"But with the assistance of McCain staff we were able to extinguish the fire around 6pm. This fire did have the potential to spread, but it was lucky McCain has a sprinkler system which activated when the fire broke out and kept everything cool.

"With the quick action by the firies and plant personnel, these three things meant that we were able to contain the fire quite quickly. It was a good result considering."

McCain Foods spokesperson Tony Rasman said damage was minimal.

"We are assessing the damage this morning and investigating the exact cause of the fire," Mr Rasman said.

"Fifty staff were evacuated as soon as the fire was detected, including some office staff, which is our normal evacuation procedure.

"We expect to be back operating shortly, hopefully by Monday. So far, only electrical cables have been found to be damaged."