More than 2,000 people were attending a three-day Jehovah's Witnesses prayer meeting at a convention center in Kalamassery, near the port city of Kochi, when the blast ripped through the crowd.
"At about 9:40 am (0410 GMT) approximately there was an explosion in Zamra International Convention Centre in which one person died and 36 are undergoing treatment," said Darvesh Saheb, director general of the Kerala police.
According to initial investigations, the explosion was triggered by an improvised explosive device, Saheb added. The Press Trust of India (PTI) news agency reported at least three "blasts" had occurred inside the convention center.
Suspected bomber surrenders to police
Hours after the incident, a man surrendered to police and claimed to be the perpetrator of the explosions. Earlier, he released a video message on social media, claiming to be a former member of the church who no longer agrees with its beliefs.
Police said they are "examining his claims and the reasons given for carrying out the act," according to The Times of India.
Jehovah's Witnesses are an international Christian denomination founded in the United States around 1870. They preach non-violence and are politically neutral, and have a history of persecution. Their activities are banned or restricted in several countries.
It is a millennial faith, meaning its members believe that the end of the world is near and that God's kingdom will soon rule over the Earth. There are nearly 60,000 Jehovah's Witnesses in India, according to the church's website.
