NEW DELHI (AP) — An explosive device blew up at a convention center in southern India killing at least one person and wounding 36 others Sunday, authorities said.

Hundreds of Jehovah’s Witness faithful were gathered for a prayer session at the Zamra International Convention Center in the town of Kalamassery in Kerala state when the explosion took place.

The state’s top police officer, Sheik Darvesh Saheb, said an initial investigation has revealed an improvised explosive device was used.

The wounded, many of them with burn injuries, were transported to hospital for treatment, he said.

Videos filmed right after the blast and shared online showed fire inside the convention center and rescuers helping people evacuate the building.

Kerala Chief Minister Pinarayi Vijayan told reporters police were investigating the “unfortunate incident.”

Police and medical personnel were put on high alert state-wide.

Jehovah’s Witnesses identify as Christians but are guided by distinctive beliefs and practices. They are known for their door-to-door proselytism.