Some 30 people have died in the U.S. city of Joplin as severe storms ripping through parts of the U.S. Midwest, global media said. Tornados swept Missouri and Minnesota on Sunday afternoon, knocking roofs off buildings. Large parts of Joplin were flattened and power and phone lines are down. A hospital has also been badly damaged. Tornado warnings and watches were posted from Texas to Michigan. On Saturday tornadoes in north-east Kansas killed one person and damaged about 20 houses. Last month at least 350 people were killed in Alabama and six other southern U.S. states as a result of storms.