At least 31 people have been killed and dozens injured by violent tornadoes in four southern US states.The twisters hit Arkansas, Mississippi, Tennessee and Kentucky at the end of a day of Super Tuesday nominating votes for November's presidential election.
A huge fire erupted at a natural gas pumping station in Tennessee that may have been damaged by the storms.
In the same state, students were temporarily trapped in the wreckage of their dormitory.
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