GUWAHATI, India (Reuters) - Police shot dead four rioters in India's northeastern state of Assam on Tuesday as security forces struggled to contain ethnic fighting that has killed at least 30 people and left riverside hamlets ablaze, forcing tens of thousands from their homes. Rioting between Bodo tribes people and Muslim settlers has raged for days in a region near Bangladesh. Some victims died of machete wounds, said aid workers who has seen the bodies. Police opened fire on rioters burning property in the Bodo-dominated Kokrajhar district, killing the four, police inspector general S.N. Singh told Reuters. Police found four more bodies in a neighboring district. "More and more villages are being burnt by attackers this evening. Violence started again in the evening after a brief lull," said a district civil servant, who asked not to be named. Earlier on Tuesday, hundreds of men armed with spears, clubs and rocks attacked an express train passing through Kokrajhar, injuring several passengers. In another incident, several people suffered bullet wounds and others were injured in a stampede when police fired to disperse a gang of 400, a senior police official said. Soldiers and federal paramilitary troops patrolled Kokrajhar town and outlying areas on armored vehicles mounted with machine guns. Some police complained they were ill-equipped to deal with the riots, despite government assurances more security reinforcements were travelling to the region. Rival mobs have spread to rural areas in three districts, targeting hamlets along river banks and in the jungle. About 500 villages have been destroyed by arson, said police. Ringed by China, Myanmar, Bangladesh and Bhutan, India's northeast is connected to the rest of the country by a narrow land strip called the chicken's neck. Home to more than 200 ethnic and tribal groups it has been racked by separatist revolts since India's independence from Britain in 1947.............. .. In recent years, Hindu and Christian tribes have vented strong anti-immigrant and anti-Muslim sentiment against Bangladeshi settlers. The Bodo tribe has clashed with Bengalis in deadly riots several times since the 1950s. Thirty years ago, about 2,000 people, mainly Muslims, died in riots in Assam.