At least 41 people were killed and over 30 injured after gunmen fired at a passenger bus in the southern port city of Karachi on Wednesday, police said.The incident occurred in the eastern district of Karachi where eight assailants fired at a bus carrying members of the Ismaili Shia community, Munir Shaikh a city police chief said.Officials fear the death toll may increase as several injured are in critical condition.Shaikh said, that according to initial reports, eight gunmen riding four motorbikes stopped the passenger bus in the Safoora Ghot area, a suburban part of eastern Karachi. They then fired from three sides, and fled.A state of emergency was declared at city hospitals.No group has claimed responsibility for the assault, the deadliest such attack since the Peshawar school carnage last year, which claimed 148 lives.