Pope Francis returns to Asia for the second time in less than six months, travelling to Sri Lanka and the Philippines in coming days to underscore his concern for inter-religious dialogue, poverty and the environment.

Security will be a main issue in both countries, particularly in the Philippines, Asia’s only majority Catholic country, where up to six million people are expected to attend an outdoor Mass on January 18.

Up to 40,000 police, troops and reservists will take part in what military chief General Gregorio Catapang has called the country’s biggest ever security operation.

“There will be soldiers rappelling up and down helicopters to rescue the pope in case he will be pinned down by a sea of people. We may airlift or use naval boats to bring the Pope to safety if necessary,” he said.

When Pope John Paul visited Manila in 1995, security perimeters were breached and he had to be taken by helicopter to a Mass site because his car could not get through a sea of some five million people.

One theme of the January 12-19 trip will be climate change. During his stay in the Philippines he will visit Tacloban, where Typhoon Haiyan killed 6,300 people in 2013.

Sri Lanka is among the Asian countries experts say will see sea level rises likely to displace people and adversely affect tourism and fisheries. The Vatican says Francis, who is preparing an encyclical on the environment, will speak about the issue several times.

While Pope John Paul made a number of trips to Asia - visiting both countries in 1995 - Francis’ immediate predecessor Benedict, who resigned in 2013, made none to a region the Vatican sees as a potential growth area.

“We have to recover the presence of a Pope in this preponderant area of humanity,” Vatican spokesman Father Federico Lombardi said. Only about three per cent of people in the region are Catholic.

“This continent in many ways represents a frontier for the Church,” said Father Antonio Spadaro, editor of the Italian Jesuit magazine Civiltà Cattolica.