Pope Francis waves to the crowd as he arrives to recite the Angelus noon prayer from the window of his studio overlooking St.Peter's Square, at the Vatican, on Sunday. AP

"I have to apologise for being late," the smiling 82-year old pontiff told crowds of faithful patiently waiting for him to appear at his study window overlooking Saint Peter's Square.

"I was trapped in a lift for 25 minutes, there was a power outage but then the firemen came," he said.

"Let's give a round of applause to the fire service," he said, prompting cheers and applause from the crowd.

Italian television networks that live-stream the Angelus had been concerned that the unprecedented seven-minute delay might have been due to health reasons.

Francis seems to have unlimited energy despite his age. But he lost part of a lung in his youth, and the occasional grimace bears witness to the sciatic pain that is a near-constant companion.

It was believed to be the first time the Vatican's head of state, who leads the world's 1.2 billion Catholics, has got stuck in a lift.

Agence France-Presse