An animal welfare group is calling for a Waikato pig farm to be investigated following the fourth fire there in a decade.

Dozens of pigs were burned to death in yesterday's blaze at the 800 square metre piggery shed.

The Fire Service says the blaze seems to have been caused by an electrical fault even though the wiring had been upgraded since the last fire.

Source: 1 NEWS

Extinguishers and hoses were the only equipment on site and Farmwatch wants to see the immediate introduction of sprinkler systems.

"How many more animals do we have to see die on this farm before it shuts down," spokesman John Darroch said, adding: "Longer term we need to see a phase out of factory farming."

The owners of the farm declined to comment but firefighters are distraught after dealing with a similar situation eight months ago when 400 pigs died in a shed fire.

"We've had four piggery fires here in the last 10 years. Whether that's common or not I'm unsure but it's certainly up there I suppose," Ngaruawahia chief fire officer Karl Lapwood said.