A fire at Washington top-fruit packer Evans Fruit Company has caused an estimated $5 million (£2.5m) worth of damage, and will shut the packhouse for as long as three weeks.

Federal investigators are looking into the fire that the company’s Tieton packing operation on Thursday.

Yakima Valley firefighters fought the fire for more than four hours, as flames spread quickly through stacks of compressed cardboard boxes. The blaze “ripped through the north end of the building and burned a section about 150 yards long”. It is estimated that between 30,000 to 40,000 boxes of apples may have been lost.

During the weekend, officials from the US Bureau of Alcohol, Tobacco, Firearms and Explosives have been sifting through the rubble for clues.

Evans Fruit Co. representatives have gone publicly on record speculating that the fire might have been the work of disgruntled ex-employees, but as yet, no police report regarding those suspicions has been filed.

Between 85 and 90 people who work at the plant will be temporarily laid off as operations shut down for the next two to three weeks.