After the collision, two angry bike borne policemen thrashed the brother-sister and also damaged their bike near station chowk under Balia police station, Balia SHO Sunil Kumar said.
The siblings have been identified as Mohan Kumar and Suman Kumari,residents of Janipur village of the district.
The incident occurred when both brother and sister were returning from Barbighi village under Balia police station after seeing the dead body of their maternal grand mother, Kumar said.
The policemen, who thrashed the duo, managed to escape from the spot after seeing the angry mob.
Stern action would be taken against the erring policemen as per the law once they (policeme) are identified, the SHO added.
Since the Chief Minister's programme was scheduled near Balia in the district today, police resorted to mild lathicharge after locals started pelting stones on them and cleared the blockade, the SHO said.