A fire at Heinz Wattie's is being treated as suspicious by fire investigation services.

Hawke's Bay senior station officer Collin Littlewood said the fire service was called out just after 2am yesterday morning to a "sprinkler alarm operation" at the King St North production facility.

"When we got there, there was lots of smoke - the sprinkler had held the fire in the area so it did not spread."

Five fire trucks from Napier and Hastings were sent, and crews with specialist equipment removed and extinguished plastic bottles and pallets that were burning in the covered area, only half of which had walls.

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"Most of it was smoke - there was a lot of paper and cardboard, but plenty of ventilation."

Mr Littlewood said the whole operation took about three and a half hours and that it was being investigated as it appeared to be suspicious.

Yesterday, police confirmed they were investigating the fire and scene examinations were taking place.

Heinz Wattie's managing director Mike Pretty said the fire was isolated to one area and that the sprinkler system operated as it was designed to do and the fire was extinguished quickly.

"We are pleased to report that no one was hurt," Mr Pretty said.

"Fortunately, there was very little damage and the factory is operating as normal."

The incident follows another that occurred in the same vicinity in the early hours of Friday morning last week when a 3m by 3m shed beside the railway line opposite Heinz Wattie's burned down.

The Hastings fire service said crews were kept busy for nearly two hours from 1.07am when the alarm was sounded.

This fire was also being treated as suspicious.

Yesterday, police were also investigating and conducting examinations at the scene of another fire in Market St North at the empty building that used to house The Warehouse, now in the process of being set up for Bunnings.

There a window was smashed, and inside a table and chair sitting in the large vacant space had been burned.

Police said they were unable to comment further on the two most recent fires.