The Cardiff Blues have lost at home to Montpellier in the Heineken Cup.
Scrum half Lloyd Williams was sent off for a spear tackle in the first half, leaving the Welsh side with just 14 men.
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People are being advised to avoid the town centre, especially Salop Road.
Feeling humid with heavy showers and thunderstorms moving north overnight into Sunday.
Four people, including three children, were taken to hospital to be checked for smoke inhalation.