Protesters in the eastern Indian state of Bihar torched trains and ransacked stations for a fourth day on Thursday in retaliation for attacks on migrants in western India, ignoring an appeal for calm by the chief minister. Police arrested more than 20 men across the state and authorities cancelled about 25 trains from state capital Patna. "The situation is very tense ... we are virtually coming to a standstill," senior railway officer Kundan Chaudhary said. "Thousands of passengers are stranded at various railway stations," he said, adding that the situation was made worse by the large number of people returning to the state to celebrate the Hindu festival of Diwali next week with their families. The migration of thousands of workers from impoverished northern and eastern states like Uttar Pradesh and Bihar into India's booming financial capital Mumbai has sparked a violent backlash, with local resentment fuelled by ambitious politicians. That in turn has provoked tit-for-tat violence in northern and eastern India, a sign of the strains that inequality is placing on society as the economy booms. On Wednesday in Mumbai, a local politician, whose arrest had sparked protests in western Maharashtra state and a backlash on migrants across the country, was given bail after spending a night in jail. Raj Thackeray, head of the small but vocal Maharashtra Navnirman Sena (MNS), was arrested on Tuesday for rioting and provoking attacks on migrants. About 50 people have been injured in clashes with the police in Bihar so far, and a 10-year old boy was killed on Wednesday by a stray bullet after police opened fire in Rohtas district. In East Champaran district on Thursday, angry mobs torched police vehicles as police beat them back with batons. The situation was now "under control", district superintendent of police N. Hasnain Khan said by telephone. In Nalanda district, protesters marched through the streets, shouting slogans and ordering shops and businesses to shut. Bihar Chief Minister Nitish Kumar late on Wednesday appealed for calm in a televised speech. "Please save Bihar," he said. Supporters of MNS, which is fuelling anti-immigrant rhetoric ahead of national and local elections due next year, had attacked north Indian railway job aspirants appearing for an examination in Mumbai on Sunday, prompting calls for Thackeray's arrest.