A hand grenade kept in a dustbin exploded at Debipukhuri Pachali area in the centre of the town with a deafening sound at 7.30 PM, Tinsukia district SP Mukdhajyoti Mahanta said.
The injured were admitted to Tinsukia Civil Hospital from where four seriously injured were sent to the Assam Medical College Hospital in neighbouring Dibrugarh district, Mahanta said.
The area has been cordoned off and investigations are on.
Early this morning, a hand grenade exploded at Duijan near here adjacent to a CRPF camp but no one was injured.
Yesterday a hardcore ULFA militant, self-styled Sergeant Major Rongmon Asom alias Mecuri, was killed in an encounter with army in Tinsukia district.