At least four persons were killed when a two-storey residential building on premises of a government primary health centre collapsed here today following an explosion which police suspect was caused by illegally stored crackers.

District Magistrate Mukesh Meshram said the blast occurred in the staff quarters belonging to a ward boy Rajesh Gautam at 3.30 PM in Kalyan puri area. Bodies of four persons, including a woman, have been retrieved from the debris.