The blast on Sunday night took place in a hub for chemical and petrochemical manufacturing units at the state's Dahej industrial estate, but its cause was not immediately clear, Reuters reported.
"The factory has been completely gutted," said Rajendrasinh Gohil, a police officer in Dahej. "Six people were charred to death."
Fire officials said they had brought under control the flames at the Om Organic manufacturing plant, about 230 km (140 miles) south of the state's commercial city of Ahmedabad.
Plant officials were not immediately available for comment.