Wearing green vestments, he spoke to a crowd of mostly young people sprawled over a hillside near the Adriatic city of Loreto on the day Italy's Catholic Church marks it annual Save Creation Day.

More than 300,000 people had slept on blankets and in tents or prayed during the night. Organisers said they were joined by some 200,000 more who arrived from throughout Italy on Sunday.

"New generations will be entrusted with the future of the planet, which bears clear signs of a type of development that has not always protected nature's delicate equilibriums," the Pope said, speaking from a white stage.

In one of his strongest environmental appeals, Benedict said: "Courageous choices that can re-create a strong alliance between man and earth must be made before it is too late."

The Pope closed the rally with a Sunday morning mass.

It was the first environmentally friendly youth rally, a break from gatherings that have left tonnes of garbage.

Participants had backpacks made of recyclable material, flashlights operated by a crank instead of batteries, and colour-coded trash bags so personal garbage could be easily recycled. Meals were served on biodegradable plates.

Tens of thousands of prayer books for Sunday's mass were printed on recycled paper and an adequate number of trees will be planted to compensate for the carbon produced at the event, many in areas of southern Italy devastated by recent brushfires.

Under Benedict and his predecessor John Paul, the Vatican has become progressively "green", installing photovoltaic cells on buildings to produce electricity and hosting a scientific conference to discuss global warming and climate change.

Benedict voiced concern about a breakdown of the traditional family and in his Sunday homily told young people to "go against the current" and challenge "seductive" media messages promoting materialism, consumerism and fleeting pleasures.