An explosion and fire at a cookie factory in central Greece killed at least four workers and left one person unaccounted for, authorities said Monday.

Axar.az reports, citing AP, aeven others, including a firefighter, were hospitalized after the blast at the Violanta biscuit plant near the city of Trikala, about 320 kilometers (200 miles) north of Athens.

The blast occurred during the night shift, and the resulting fire gutted the plant. Fire crews battled the blaze for hours before recovering four bodies — all women — from the destroyed building.

Police said investigators suspect the explosion may have originated near the ovens, which operate around the clock. Six workers and one firefighter were being treated at a hospital in Trikala, none in serious condition.

Arson investigators and emergency crews remained at the scene as authorities worked to determine what caused the explosion.