Toronto — Surrounded by a sea of young Catholics camping on a former Canadian Forces base, John Paul II played the role of stern biblical prophet Saturday, warning of a world being taken over by technology and efficiency without reference to human spirituality.

"The question that arises is dramatic," he said, his voice echoing off the one-time hangars at the former Downsview base in the northwest corner of Toronto while hundreds of thousands of hushed World Youth Day delegates sat on the wild grass and listened.

"The question will not go away: on what foundations, on what certainties should we build our lives and the life of the community to which we belong?

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"On what foundations must we build the new historical era that is emerging from the great transformations of the 20th century? Is it enough to rely on the technological revolution now taking place ... without reference to the individual's spiritual dimension or to any universally shared ethical values?

"Is it right to be content with provisional answers to the ultimate questions, and to abandon life to the impulses of instinct, to short-lived sensations or passing fads?"

The Pope said the 20th century has often tried to do without the cornerstone of Christianity and Christian teaching. But he said any attempt to build the city of man without reference to Him would "actually [be] building that city against man."

"Christians know that it is not possible to reject or ignore God without demeaning man."

As dusk fell, a hundred thousand points of light flickered across the park from candles held by the young people. A huge red-lit cross, 55 metres high, dominated the horizon.

A Toronto radio station's helicopter crew estimated that between 450,000 and 500,000 people were gathered at Downsview, now a federal park. The number seemed unlikely. There are only about 200,000 registered delegates for the Roman Catholic Church's World Youth Day.

The scene bore a strong similarity to a summer music festival, with some people in tents and makeshift shelters — constructed of plastic and, frequently, national flags — and others lying on the grass beneath the open sky.

One hangar was turned into a hospital. Another was a giant field kitchen, producing sandwiches, salads and hot stew. A third was used as a media centre for the 3,800 journalists filming and reporting on the event.

Beyond a few drops of rain, a forecast storm didn't materialize. The Pope arrived by helicopter at about 6:30 p.m. from Morrow Park, a retirement home for nuns on the east side of the city where he is staying.

He held brief meetings at Morrow Park with Governor-General Adrienne Clarkson, Prime Minister Jean Chrétien and Ontrio Premier Ernie Eves. Mr. Chrétien also turned up at Downsview to schmooze the crowd and hear the Pope speak.

The young people are to observe an overnight vigil of prayer and spiritual preparation for Sunday's mass celebrated by the Pope — the final event of the week-long World Youth Day gathering.

The mass is open to the public. Organizers expect up to one million people to attend.