Police used lathis, tear gas and water cannon after cops blocked the BJP’s march to CM Mamata Banerjee's office in Kolkata. Clashes broke out between the West Bengal Police and BJP workers in Kolkata on Thursday as the saffron party workers tried to break through barricades during their march towards state secretariat Nabanna on Thursday. Thousands of BJP workers from Kolkata and Howrah began marching towards Nabanna to protest the "worsening" law and order in the state.