At least two people were killed and two injured on Saturday, when oxygen cylinders exploded in a plant near Orissa's Rourkela city, police said.The accident took place at the Asiatic Gases Ltd. plant at Vedvyas, about 500 km from Bhubaneswar."Two people have died and two suffered critical injuries," Superintendent of Police Deepak Kumar told IANS. One person is still trapped inside the plant, he said.