A violent attempt to pull down a wall in Maheshtala, South 24-Parganas, led to clashes between two groups that escalated into stone pelting on police and retaliation with tear gas on Wednesday afternoon.
At least 19 police personnel were injured, including a divisional deputy commissioner. Several police vehicles were damaged.
Kolkata Police’s deputy commissioner (Port), Harikrishna Pai, was admitted to hospital with multiple injuries.
Senior officers said there were no reports of any civilians being injured.
At least 18 alleged rioters had been arrested till late on Wednesday.
The clash that broke out in Maheshtala, under Rabindranagar police station, spread to Nadial in the Kolkata Police area. Police reinforcements from Howrah, Bidhannagar and Barrackpore commissionerates rushed to the spot.
Eyewitnesses said the clash erupted when some people tried to set up a fruit stall in a public place and started vandalising the area when prevented.
The incident happened close to Rabindranagar police station. But the police were initially outnumbered.
“We used tear gas to disperse the crowd. No civilians were injured,” said an officer.
The crowd that dispersed from Maheshtala moved to the Nadial-Rajabagan area, turning the place into a virtual battlefield targeting the police.
Sources said the group that started the violence in Maheshtala continued it in Nadial-Rajabagan, making the police suspect a planned attack.
“They were armed with stones and bricks. It is difficult to get hold of so many bricks and stones unless it is planned in advance. A detailed probe has been started,” said a senior officer of Kolkata Police.
Many rioters were seen throwing stones from rooftops, prompting the police to aim tear gas shells higher.
The cops said video footage was being analysed to identify the men seen instigating the mob and hurling stones.
Kolkata Police commissioner Manoj Verma and senior officers of the city police, including additional commissioner DP Singh, visited the spot.
Kolkata Police and the adjoining Bengal Police areas have started mobile patrolling in the affected areas.
Police pickets were set up to prevent further violence, which many believe could have been contained sooner had a larger force been present initially.