A fire at Silver Fern Farms' Whakatu meatworks was caused when blood and bone on a drying line unexpectedly ignited.
Fire Service central communications shift manager Murray Dunbar said the blaze broke out in a boiler room at 4am yesterday and spread to the roof.
Seven fire crews attended the Ranitane Rd plant after a private alarm was activated, Mr Dunbar said.
The blaze was extinguished about 6am by fire crews from Hastings, Napier and Haumoana.
Hastings Fire Brigade incident commander Collin Littlewood said during the process of drying blood and bone product at the plant, the product moved along a drying line and passed through a metal augur, which could become extremely hot.
In this case, the blood and bone caught fire.
"It was quite a small fire but it was very difficult to put out."
Silver Fern Farms' communications manager Justin Courtney said a small team of about 20 cleaning and engineering staff were on site at the time.
They were evacuated during the fire in line with company procedure and were "all safe", Mr Courtney said.
Production resumed at the plant at 8.30am, which was two hours after its normal start time.
Damage to the plant was described as minor.
"Everything is operating as it should, with rendering being carried out off-site."
Hastings Fire Brigade station officer Michael Manning said after the Fire Service was advised the plant's alarm had been activated, it also received several calls about the fire from workers at the site.
The Fire Service had to cut away parts of the plant's roof to enter the ceiling space. No injuries were reported.