Calcutta, May 12 :    Calcutta, May 12:  A woman and a four-year-old boy, were killed and at least five others seriously injured in a string of road mishaps on Saturday. The mob smashed and set the killer vehicles ablaze. Four-year-old Mohammad Shahbaj, of Gas Street, was knocked down by a Matador van around 9.30 am at the Gas Street-Raja Dinendra Chandra Street crossing. Shahbaj was taken to NRS Medical College and Hospital, where he was pronounced dead. Hundreds of people gathered at the spot and gheraoed the traffic sergeant. They beat up the van driver and blocked the road for about half an hour. The vehicle was impounded and the driver arrested. Kiran Soni, a 30-year-old homemaker, was run over by a government bus at the crossing of Madan Chatterjee Street and Central Avenue in the afternoon. The bus lost control and hit her while she was crossing the street. Soni was pronounced dead at Calcutta Medical College and Hospital. Local people damaged the bus. The driver is absconding. A bus was set ablaze in front of Jyoti Cinema on Lenin Sarani after it hit a rickshaw in the evening. Three fire tenders brought the blaze under control, said officials of Taltala police station. The vehicle was impounded. About 100 Trinamul Congress supporters, led by Montu Sanyal and Paresh Pal, held a sit-in on Bagmari Road, in the Maniktala police station area, in the afternoon to protest police inaction in quelling poll violence. The road block was lifted after two hours. later after police officers promised to look into the matter.