Pope Francis has said he was late to his weekly Angelus prayer because he had been stuck in a Vatican elevator and had to be freed by fire fighters.

"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 St 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.

The Pope also today called on individuals across the world to make changes to their daily habits to stop climate change in its tracks, and to put pressure on their leaders "before it's too late".

"We have created a climate emergency, which seriously threatens nature and life, including our own," he said in a message to mark this year's World Day of Prayer for the Care of Creation.

"This is the time to reflect on our lifestyles and how our daily choices in terms of food, consumption, travel, use of water, energy and many other material goods are often reckless and harmful," he wrote.

Francis, a long-time environmental campaigner, said his plea went out to "every member of the human family".

"Let us choose to change, to take on simpler and more respectful lifestyles."