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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Showers in the north will spread southeastwards overnight. Temperatures will be higher so not as chilly as list night.
Chilly start to Tuesday, turning into a largely fine and dry day.
Political Editor Adrian Masters was joined in the studio by assembly members Bethan Jenkins, Mick Antoniw and Suzy Davies.