MANILA (AFP) - Pope Francis will immerse himself in some of Asia's most fervent Catholicism during a trip to Sri Lanka and the Philippines starting on Tuesday, with millions of devotees set to turn out.

The Argentinian pontiff with a man-of-the-people reputation could attract one of the biggest gatherings ever for a pope during an open-air mass in the Philippine capital of Manila on Jan 18. The event may draw up to six million people, offering a pulsating example of Asia's status as a dynamic growth region for the Catholic Church - but also creating a security nightmare.

The pope's trip, which begins in Sri Lanka, comes just five months after he visited South Korea, signalling the huge importance the Vatican places on Asia and its potential for more followers.

"This second trip to Asia... is a message in itself for this great continent. It is necessary to have the pope return to this important part of the world," Vatican spokesman Father Federico Lombardi said as the 78-year-old pontiff prepared for the week-long visit.

In Sri Lanka, the pope will preach reconciliation as the majority Buddhist nation of 20 million people continues to endure ethnic conflict following the end in 2009 of nearly four decades of civil war that pitted separatist Tamils against Sinhalese.

Religious violence has continued since then, with attacks on mosques and churches by nationalist Buddhist groups who say minorities have undue influence on the island.

But the pope will land in Sri Lanka just days after Maithripala Sirisena scored a stunning peaceful election victory over veteran strongman Mahinda Rajapakse, a result that offers hope for future peace prospects.

During his two-night stay, the pope will visit a church that sheltered refugees from across the religious and ethnic divide during the civil war, and which has a 450-year-old statue of the Virgin Mary.

The centrepiece of the visit will be a public mass on the sea front in the capital of Colombo, which is expected to attract one million Catholics and followers of other religions.

Sri Lanka has a sizeable Catholic minority of about 1.5 million - but it is when Francis reaches the Philippines on Thursday that he can expect to feel the most vibrant and colourful forces of the region's Catholic faith.

- Excitement -

The Philippines is one of the Church's modern success stories, counting roughly 80 per cent of the former Spanish colony's 100 million people as Catholics, which has helped to offset waning influence in Europe and the United States.

Anticipation has been building for months ahead of his trip - the fourth papal visit to the Philippines - with the pope dominating the media, billboards and sparking a merchandise frenzy.

"I'm excited, because this pope's focus is on the poor," said human resources manager Renita Terciano, 50, who has booked hotel rooms near the Manila papal mass park venue for her family so they can attend the event.

If the crowd is as big as expected, it could surpass the estimated five million people who turned up for a mass by Pope John Paul II at the same venue in 1995. That event is regarded as the biggest ever gathering to see a pontiff.

Church officials say the pope's visit is also a "mercy and compassion" trip to meet survivors of Super Typhoon Haiyan, which claimed 7,350 lives when it destroyed entire farming and fishing communities in impoverished areas of the central Philippines in 2013.

The pope will spend Saturday in Tacloban, one of the worst-hit cities, and nearby areas. He is due to give a mass to tens of thousands of typhoon survivors at Tacloban airport, and have a private lunch with a small group of others.

Erlinda Suyom, 30, who lost her two children and her home near Tacloban to tsunami-like waves, said she would dearly love to meet the pope.

"I would like to ask for his guidance. I also want to tell him to ask God to ensure that my son and daughter are happy in heaven," Suyom told AFP.

- Security -

Security will be a major issue throughout the pontiff's Asia trip, but Philippine Church officials have said he will not travel in a bulletproof "popemobile" because he wants to be closer to his flock.

Philippine authorities have said they are deploying nearly 40,000 security personnel in one of the nation's biggest ever security operations.

"We are doing everything humanly possible to secure the safety of the pope," Philippine presidential spokesman Edwin Lacierda told reporters, while stressing authorities had not detected any specific threat.