After getting information about the incident, police officials reached the spot to ascertain the facts.
According to police sources, one person has been detained in connection with the incident.
A loud explosion took place a few metres away from where the chief minister was addressing the gathering.
No casualties have been reported in the incident. Further details are awaited.
Notably, on March 27 this year, a man was arrested in Bihar for trying to attack Chief Minister Nitish Kumar. The incident occurred at Bakhtiyarpur block in Patna district, where Nitish Kumar was paying floral tributes to the statue of a freedom fighter from the area.