Commissioner of Police, Barrackpore Police Commissionerate, Neeraj Singh said the accident took place when the school children were waiting for a bus on the side of Belghoria Expressway at around 9 AM.
Three children died on the spot while another was critically injured and taken to the hospital, Singh said adding that the injured child might lose one leg even if he survives.
The victims were in the age group of 5-8 years.
An irate mob immediately set three police vehicles afire, smashed a RT van and put up a road blockade, while the police were trying to pacify them.
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The truck driver managed to flee and till evening he was absconding, even as search operations were on to nab him, police said.
West Bengal Chief Minister Mamata Banerjee described the incident as "very sad", leading to loss of three lives from the same family.
The state Home Department has sought a complete report from the Director General of Police.
Meanwhile, instructed by the Chief Minister, state Food Minister Jyotipriyo Mallick and Tourism Minister Bratya Basu visited the victim's house to console the family.
The ministers also offered the family members complete cooperation from the government including jobs in local municipal body if they were willing.