Pope Leo celebrated the largest event yet of his nearly three-month tenure on Sunday, encouraging a crowd of more than a million Catholic young people gathered in a field on the outskirts of Rome to spread their faith.

Young people from more than 146 countries, some wearing colourful bandanas to ward off the hot summer sun, were pressed against fences in the Tor Vergata field as Leo toured the crowd in his white popemobile in late afternoon.

In his closing blessing for the Jubilee of Youth, Leo remembered the young people of Gaza and Ukraine and other countries "bloodied by war" who could not join their celebration.