The 12-year-old girl from Ernakulam district, who was among the over 50 people injured in the blast, died at the Kalamassery Government Medical College Hospital, NDTV reported. Earlier, two women had also died in the blast at the convention centre.
The girl was admitted to the hospital with severe burns covering 95 per cent of her body, NDTV said.
The explosion was reported at 9.40am local time on Sunday at the town’s Zamra International Convention & Exhibition Centre, said Kerala’s highest-ranking police official Shaik Darvesh Saheb.
“Preliminary investigation shows it is an IED device and we are investigating it,” he said, adding that he was going to the area himself to oversee investigations.
The top police official said “a special team will be constituted today” to lead the investigations. He also warned people against sharing provocative posts on social media.
Police said a man had surrendered at a police station and claimed responsibility for the attack.
The suspect was identified by police officer MR Ajith Kumar as Dominic Martin. “The person named Dominic Martin has submitted some evidence which we are examining. He claims to be a member of the Jehovah’s Witnesses church,” he said.
Authorities did not elaborate on a possible motive for the attack, which remains unknown.
Kerala’s chief minister Pinarayi Vijayan, who is currently in Delhi, called the incident “unfortunate” and promised a thorough investigation.
“It is an unfortunate incident. One person died and two others are in serious condition. An investigation has been launched and further details will be available later,” he told reporters in the national capital.
Earlier there was confusion over the number of blasts. Initial media reports said a series of explosions had struck the prayer meeting minutes after it began.
Videos from the convention centre showed people screaming and running, with toppled chairs as a fire swept parts of the convention centre.
State minister VN Vasavan also claimed at least two consecutive blasts took place.
“It is an unusual accident. All agencies are here for preliminary examination,” said Mr Vasavan.
Health minister Veena George said 52 people were admitted to different hospitals. Eighteen people were in intensive care units and five were critical.
India’s federal counter-terrorism unit, the National Security Guard (NSG), rushed one of its bomb disposal units from the capital Delhi to Kerala to collect materials from the blast site and conduct an investigation.
A forensic team from the country’s anti-terror agency, the National Investigation Agency (NIA), has also reached the site to collect evidence.
Federal home minister Amit Shah said he spoke with Kerala’s chief minister and discussed the situation in the state after the bomb explosion.
He said he has instructed the NIA and NSG federal investigative agencies to reach the spot and assist in investigations.
V Muraleedharan, a junior minister in the External Affairs and Parliamentary Affairs ministries, suggested the blast could be considered a “terrorist act” and claimed the incident would shock the Christian community in Kochi city, about 23km away from Kalamassery, where the attack occurred.
“It is disturbing to note that Kerala is becoming a place where such incidents are happening which are considered a terrorist act,” he said.
Police sources cited by the NDTV news channel said the explosives were placed in a tiffin box.
Police in Delhi were also placed on high alert after the blast in Kerala. It comes during the peak of the Hindu festival season, with businesses and families in India preparing for the upcoming festivities of Diwali.