Rourkela: Four labourers were killed and seven others injured, four of them critically, when the auto rickshaw in which they were travelling collided with an iron ore laden truck in Odisha`s Sundargarh duistrict, police said on Sunday. The incident took place near K Bolang in Bonai sub-division yesterday when the labourers were on their way to work. The truck collided head on with the auto rickshaw killing the four on the spot, the police said. All the injured were admitted to a local health centre and later the four grievously wounded ones were shifted to Rourkela hospital as their condition turned critical, the police added.