Pope Francis drew a record six million people as he celebrated mass in the rain-swept Philippine capital Sunday, a triumphant finale to an Asian tour in which he championed the plight of the poor.

Filipinos are famous for practising a passionate brand of Catholicism and they turned out in a celebratory mood that defied the gloomy skies, determined to see the charismatic 78-year-old pontiff.

Francis made an exhilarating entrance to a Manila bayside park for the mass aboard a "popemobile" that was styled after the nation's iconic, flamboyant and much-loved "jeepney" minibus.

Dressed in a plastic yellow poncho, he waved and smiled to wildly cheering crowds, stopping repeatedly so he could lean over barriers and kiss babies, before reaching the sea of believers at Rizal Park.

The Philippines is famed as the Catholic Church's bastion in Asia, with 80 percent of the former Spanish colony following the faith.

But even the pope was stunned at the size of the crowd which he looked out on from the stage.

"I cannot fathom the faith of the simple people," Francis said, according to the Archbishop of Manila, Cardinal Luis Antonio Tagle, who acted as the pontiff's chaperone.

Six million turned out to see the pope at the park and along motorcade routes, the head of Manila's planning agency, Francis Tolentino, told AFP, adding this was based on calculations done with the police.

This surpassed the previous world record for a papal gathering of five million during a mass by John Paul II at the same venue in 1995.

Vatican spokesman Federico Lombardi said Sunday's crowd could even reach seven million. However he did not have any firm assessments to base this on.

- 'Gift of God' -

Perla Ponce, 76, a retired nurse who travelled hundreds of kilometres from her home in the southern Philippines, said she felt "euphoric" to have seen the pope and been a part of the mass.

"You can't describe the feeling. It's just like you have met Jesus Christ himself," a rain-soaked but beaming Ponce told AFP.

Volunteer rescue worker Kristine Bancure had been on duty as a medic through the day but also got a glimpse of the pope.

"It's an overwhelming feeling. I felt the hair on my skin standing up," she said.

In his homily, the pope praised Filipinos for their reverence.

"The Philippines is the foremost Catholic country in Asia. This is itself a special gift of God, a blessing," the pontiff told the vast crowd.

"But it is also a vocation. Filipinos are called to be outstanding missionaries of the faith in Asia."

He also spoke out against "poverty, ignorance and corruption", a theme he has focused on repeatedly during his five-day visit to the Philippines.

In his first speech of his tour, at the presidential palace, Francis lectured the nation's politicians to show integrity and end "scandalous social inequalities".

About 25 million Filipinos, or one quarter of the population, live on the equivalent of 60 cents a day or less, according to government data.

- Emotional meeting -

Before the mass, the pope had an emotional encounter with former street children at an event at a Catholic university.

Glyzelle Palomar, a 12-year-old taken in by a church charity, wept as she asked how God could allow children to descend into prostitution and drug addiction.

The pope folded her in his arms, and discarded his prepared speech as he reverted to his native Spanish to deliver an impromptu and heartfelt response.

"She is the only one who has put a question for which there is no answer and she wasn't even able to express it in words but in tears," he told those gathered at a Catholic university in Manila.

The pope called on people to show tangible, genuine concern for the poor and marginalised.

"(There are) certain realities in life we only see through eyes that are cleansed with our tears," he said.

- Typhoon trip -

The pope said the main reason for visiting the Philippines was to meet survivors of Super Typhoon Haiyan, the strongest storm ever recorded on land which claimed more than 7,350 lives in November 2013.

He flew on Saturday morning from Manila to Leyte island, ground zero for the typhoon, and celebrated a deeply emotional mass with 200,000 survivors.

"Long live the pope!" the crowd chanted before the mass.

Francis had planned to spend a full day in communities where homes were flattened by monster winds and tsunami-like ocean surges, but was forced to return to Manila to avoid another tropical storm.

Still, he was deeply moved by his truncated time in the typhoon areas and felt privileged to have made the trip, Cardinal Tagle told reporters.

The pope's tour, which also took him to Sri Lanka, was his second trip to Asia in five months, in a nod to the region's growing importance for the Church as it faces declining support in Europe and the United States.

It was also the fourth papal visit to the Philippines, and the rapturous reception given to him throughout his stay cemented the nation's status as the Church's Asian role model.

The pope will fly back to Rome on Monday morning.