Four persons were killed and 40 severely injured when a luxury bus rammed into a truck near Howrah district in West Bengal on Saturday, police said."A luxury tourist bus rammed into a truck, loaded with iron rods, on the National Highway 6 in the morning. The bus was on its way back from Puri to Kolkata," police said.According to police, the bus was travelling at a very high speed and the iron rods pierced the vehicle.Lack of visibility due to fog might have caused the accident, it said.The injured tourists were admitted to Uluberia Hospital in Howrah."The driver and the helper of the bus fled after the incident. We are hunting for the two," police added.