The A39 is closed in both directions due to an accident between the entrance to the Royal Cornwall Showground and Tredruston Road.
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It will be dry and bright in the morning but as the day goes on it will become wet and very windy.
Eastern parts will have heavy rain in the morning, clearing by afternoon.
Fire and Rescue Service says it received a 999 call to say there had been an explosion in a third floor flat within a mid terraced building.