Hopefuls trying their luck will perform in front of producers and if they impress they'll sing for the judges later in the competition.
Returning host Dermot O'Leary who is in Cardiff for the auditions, said: "As always I'm looking forward to the laughs, the hugs, maybe not so much the tears, and watching really talented people... and some not-so-talented people.
"But that's the beauty of the show - you never know who's up next."
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Cardiff's Neonatal Intensive Care Unit has been closed since Thursday due to poor 'infection control measures', a health council has said.
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The widow of Welsh rugby player Danny Jones will sing the traditional Challenge Cup hymn 'Abide With Me' at Wembley Stadium tomorrow.