About 50 pigs died after fire tore through a shed on a piggery farm in the Waikato on Friday.

The fire at Brien​ Farms in Hopuhopu comes eight-months after a similar blaze which saw 400 mother and baby pigs burned to death. And in April 2005, under different owners, 300 pigs were burned to death.

Multiple people reported the blaze, at the Great South Road site north of Ngaruawahia, to the fire service about 8am.

GEORGE HEARD/FAIRFAX NZ Approximately 50 pigs died in a fire in Hopuhopu. The Brien Farms piggery has had two previous fires - one in 2005, under another owner, and one in 2015.

Ten fire engines, including three water tankers, fought the large fire at the Hopuhopu piggery.

READ MORE: * Mother and baby pigs burned to death in blaze

The 800-square-metre building housed sows who were farrowing, or recently given birth.

Ray and Joanne Brien have owned the operation on Great South Rd for less than a year.

They had taken up pig farming after selling a dairy farm they owned near Otorohanga.

In August, Joanne Brien said she left Otorohanga "for a better life, but since we have been here we have had nothing but trouble with equipment failures and all sorts of things."

The Briens and their employees were working when the fire broke out.

They were too upset to speak to media but issued a statement through family member Julie Brien.

"Our family and employees... are very distressed and saddened that we have lost some of our animals and property. We're very concerned that this has happened," the statement said.

They were in shock and focussing on supporting their employees and other stock on the farm.

A fire safety investigator and insurance assessors had been on site and the farm planned to make a further statement on their plans once the fire's cause was determined, Brien said.

Waikato fire safety officer Kevin Holmes was at the farm on Friday.

"We're still investigating but it's highly likely the cause of the fire was electrical."

He also confirmed there were no sprinklers in the building where the fire happened.

The Briens suspected the 2015 fire was caused by an electrical fault too, even though the building was about five years old.

John Darroch from Farmwatch New Zealand, said he was not surprised by the extent of the fire.

"Given (my) two previous visits, I was not surprised to hear of the fire. There were no sprinklers or a fire extinguisher."

Darroch visited the Hopuhopu pig farm before the Brien's took over in 2015. He has not visited since.

"The condition of the place when I went there, it was dilapidated," he said.

"There were rats running across the wiring which was a safety hazard.

"You know, I read the last story with the owners who said they were traumatised when the [2015] fire happened, but yet, it's happened again. These animals are completely vulnerable when a fire happens - look at what's happened today.

"Animals will always be vulnerable as long as there are factory farms."

SPCA chief executive Ric Odom said the fire was a tragedy and highlighted the need for animal emergency planning.

* It was initially reported 700 pigs had died.

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