A high-intensity blast ripped apart the staff quarters of a public health centre at Kalyanpur in central Uttar Pradesh’s Kanpur district on Thursday, killing at least three persons.
At least 15 people, including children, were feared trapped under the debris.
The blast, however, did not damage the health centre, which was packed with patients.
Though the police ruled out a terror angle, the Anti-Terrorist Squad was carrying out investigations with the local police.
The explosion could have been the result of a burst cylinder or illegal firecrackers stored in the quarters going off, the police said.
Units in Kalyanpur and areas around are known to store and make firecrackers, particularly in the Diwali season.
In the past week, five people have lost their lives in explosions at units making firecrackers illegally in the area.
Kanpur district magistrate Mukesh Meshram said rescue efforts were on and four critically injured persons were taken to hospital.
Aditya Tripathi, who was near the site of the blast, said, "The sound was deafening. Everyone watched in shock."
Sushant Pandey, an engineering student, said the nearby motorcycle repair shop he was at shook after the explosion. "I pulled out at least four people from the debris and heard shrieks of children stuck inside," he said.