Pope Francis said on Sunday men should listen to women's ideas more and not be male chauvinists.

The Argentine pope made impromptu remarks during a youth rally at a co-ed Catholic university in the Philippine capital, Manila, after he noted that four of the five people who addressed him on stage were male.

"There is only a small representation of females here, too little," he said, bringing laughter from the crowd.

"Women have much to tell us in today's society. At times we men are too 'machista'," he said, using the Spanish term for male chauvinists.

"(We) don't allow room for women but women are capable of seeing things with a different angle from us, with a different eye. Women are able to pose questions that we men are not able to understand," he said to more applause.

He noted that it was a 12-year-old girl, not any of the four men, who had posed the toughest question, asking why God allowed children to be abandoned..

He ended that part of his impromptu remarks with a joke: "So, when the next pope comes to Manila, let's please have more women among you."

Francis has said that, while the Roman Catholic Church's ban on women priests is definitive, he wants to appoint more nuns and other women to senior positions in the Vatican.

Also on Sunday, the pope said a huge open-air Mass for a rain-drenched crowd of millions in the Philippine capital, after appealing to the world to "learn how to cry" over the plight of poor, hungry, homeless and abused children.

City officials said some 4 million people were in Manila's Rizal Park and more in surrounding areas to witness the event that caps Francis's week-long trip to Asia.

The 78-year-old Pope, wearing a transparent yellow poncho over his white cassock, was driven through the ecstatic crowd in a "popemobile" modified from a jeepney, the most popular mode of transport in the Philippines.

He stopped often along the route to kiss children and bless religious statues on the day the Philippines celebrates the feast of the infant Jesus. The faithful, also wearing ponchos, held up rosaries in a forest of uplifted arms as he passed by.

Some people in the capital of Asia's only predominantly Catholic country had waited during the night for gates to open at dawn. The gates opened nine hours before the start of the Mass, which was due to last nearly three hours.

In his homily, the Pope urged Filipinos to shun "social structures which perpetuate poverty, ignorance and corruption", a theme he stressed when he held talks with President Benigno Aquino on Friday. Aquino attended the Mass. 

Francis also took another swipe at the government's population control efforts, saying the family was under threat from "insidious attacks and programmes contrary to all that we hold true and sacred".

Organisers had said they had expected as many as 6 million people, more than the 5 million who flocked to a Mass there by Pope John Paul 20 years ago.

The Pope said he was moved by the question earlier posed by the 12-year-old girl, who had herself been abandoned.

"Many children are abandoned by their parents. Many of them became victims and bad things have happened to them, like drug addiction and prostitution. Why does God allow this to happen, even if the children are not at fault? Why is it that only a few people help us?" the girl, Glyzelle Iris Palomar, asked him.

STREET CHILDREN

The girl, who was rescued and found shelter in a Church-run community, broke down in tears and could not finish her prepared welcome. The Pope hugged her and later put aside most of his own prepared speech to respond.

"She is the only one who has put forward a question for which there is no answer and she was not even able to express it in words but rather in tears," he said, visibly moved.

"Why do children suffer?" the Argentine Pope said, speaking in his native Spanish. An aide translated his words into English for the crowd of about 30,000 young people on the grounds of the Church-run university.

"I invite each one of you to ask yourselves, 'Have I learned how to weep ... when I see a hungry child, a child on the street who uses drugs, a homeless child, an abandoned child, an abused child, a child that society uses as a slave'?" he said.

Children can be seen living on the streets of the Philippine capital, as they often do in many poor Asian countries, surviving by begging and picking through garbage in vast dumps.

The United Nations says 1.2 million children live on the streets in the Philippines. According to theChild Protection Network Foundation, 35.1 percent of children were living in poverty in 2009, the last year such data was available. Nearly 33 percent of Filipinos live in slums.

In his homily later at the Mass, the Pope again spoke of the need to defend children, saying: "We need to see each child as a gift to be welcomed, cherished and protected. And we need to care for our young people, not allowing them to be robbed of hope and condemned to life on the streets."