UPDATED 4.03PM A fire at Waikato Pig farm this morning is being used as a reminder to farmers, to have an escape plan for their animals.

A specialist fire investigator is at a piggery where 50 animals have perished in a fierce blaze.

Northern Fire Service shift manager Jaron Phillips said firefighters could not save the pigs housed in a building used for farrowing.

"Out of the 700 pigs on site 50 have been killed," he said.

SPCA CEO Ric Odom said animals contained in sheds are completely reliant on their farmers.

He said this means it's essential for farmers to be prepared for a fire as it could save many animals their lives.

"Have really good detection systems so if something does happen you know about it straight away. And then have a really effective plan in place to move the animals out of that danger area".

At its height 10 fire crews were at the scene of the Hopuhopu fire north of Ngaruawahia.

The specialist investigator was now at the scene as crews dampened down what was left of the badly damaged building.