Nige Harper uploaded this photo to Twitter. He says the river Gwenfro on Caia Park is threatening to burst its banks.
It's after heavy rain in the area.
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Prime Minister Theresa May announced the decision from Downing Street.
A fairly cloudy night to come with hill and coastal fog lingering in places. This could be thick enough for the odd spot of drizzle.
Father-of-three Nick Bickerstaff, from Denbighshire, was waiting for daughter Ellen and her friend in the foyer at the end of the concert.