Pope Francis ended his Asian pilgrimage with an appeal for the future of the Catholic Church, urging an estimated three million rain-soaked Filipinos to protect their young from sin and vice so they can instead become missionaries of the faith.

Pope Francis marked an important Filipino feast day honouring the infant Jesus by dedicating the final homily of his week-long Asian trip to children.

It was a reflection of the importance that the Vatican places on Asia as the future of the church since it is one of the few places where Catholic numbers are growing - and on the Philippines as the largest Catholic nation in the region.

"We need to see each child as a gift to be welcomed, cherished and protected," Pope Francis said in his homily. "And we need to care for our young people, not allowing them to be robbed of hope and condemned to a life on the streets."

Photo: Reuters

Pope Francis earlier made a triumphant entry into Manila's Rizal Park in his popemobile, wearing the same cheap, plastic yellow rain poncho handed out to the masses during his visit to the typhoon-hit city of Tacloban a day earlier.

The crowd - a sea of humanity spread out across 148 acres of parkland and boulevards surrounding it - erupted in shrieks of joy when he drove by, a reflection of the incredible resonance Pope Francis's message about caring for society's youngest and most marginal has had in a country where about a quarter of its 100 million people lives in poverty.

Organisers had expected that as many as six million people might turn out, surpassing the five million record set by St John Paul II at the same park in 1995. Two hours before the start of Mass, the chairman of the Metropolitan Manila Development Authority, Francis Tolentino, reported that three million had packed the area.

But with a steady rain falling, people were seen turning around along one of the main boulevards leading to the park and heading away.

Earlier in the day, Pope Francis drew an estimated 200,000 people to Manila's Catholic university, where he came close to tears hearing two rescued street children speak of their lives growing up poor and abandoned.

Pope Francis has dedicated his four-day trip to the Philippines to the poor and marginal. He has denounced the corruption that has robbed them of a dignified life, visited with street children and travelled to the eastern city of Tacloban to offer prayers for the survivors of the deadly 2013 Typhoon Haiyan, which devastated one of the Philippines' poorest regions.

Pope Francis ditched his prepared remarks at the university, speaking off the cuff to respond to 12-year-old Glyzelle Palomar, who wept as she asked Pope Francis why children suffer. She spoke of children who are abandoned or neglected by their parents and end up on the streets using drugs or in prostitution.

"Why is God allowing something like this to happen, even to innocent children?" Palomar said through tears. "And why are there so few who are helping us?"

A visibly moved Pope Francis said he had no answer. "Only when we are able to cry are we able to come close to responding to your question," he said.

"Those on the margins cry. Those who have fallen by the wayside cry. Those who are discarded cry," he said. "But those who are living a life that is more or less without need, we don't know how to cry."

And he added: "There are some realities that you can only see through eyes that have been cleansed by tears."