The four from Bangor's Cor Glanaethwy were freed by the fire service at 11:45 BST, half an hour before rehearsals were due to start at Wembley.
Musical director Cefin Roberts said they had been "sending us selfies from the lift to say they're ok".
"It's quite a drama at the moment."
Mr Roberts told BBC Radio Wales: "They've entertained the rest of the people stuck with them in the lift."
Four members of a north Wales choir spent two hours stuck in a lift at their London hotel, disrupting their preparation for the first live semi-final of Britain's Got Talent.