A forensic team and sniffer dogs have been sent to the spot to ascertain the nature of explosion.
Five people, including a woman and a child, were injured in an explosion in front of a multi-storey building in the Nagerbazar area in Kolkata's northern suburbs on Tuesday, police said.
The explosion was reported outside a fruit shop on the ground floor of the building in the congested Kazipara area under the jurisdiction of Dum Dum Police Station around 9 am, a police officer said.
The injured have been rushed to the state-run R G Kar Medical College and Hospital, he said.
A forensic team and sniffer dogs have been sent to the spot to ascertain the nature of explosion, police said.
"Initially, we thought it was a gas cylinder blast. But it is not so. We are trying to find out the details. Forensic experts, along with the CID bomb disposal squad, are examining the area," a senior officer of Barrackpore City Police Commissionerate said.
The building also houses the office of South Dum Dum Municipality Chairman Panchu Roy, who claimed that he was the actual target of the blast.
Mr Roy, stopping short of naming any political party, said the forces, which are currently attacking the ruling TMC all over Bengal, are behind the attack.
"It was a pre-planned blast... They had planned to kill me and other TMC workers, as it would create panic and help them gain foothold in the area," he told PTI.
He also claimed that the number of injured people was 10.
Asked whether the explosion was a result of infighting within the TMC, Mr Roy said there was no such issue in south Bengal.