Pope Francis has arrived in the Indonesian capital Jakarta, kicking off the longest and farthest trip of his tenure to the Asia Pacific region.

He is expected to highlight environmental concerns and the importance of interfaith dialogue during the 12 day trip, which will also see him travel to Papua New Guinea, Singapore and Timor-Leste - the only one of the four countries that is predominantly Catholic.

It's a particularly challenging journey for a man who turns 88 in December and has been battling a spate of health issues.

Asia Pacific is one of only a few places in the world where the Catholic Church is growing in terms of baptised faithful and religious vocations.

Parts of the Pope's trip, which was originally scheduled in 2020 but postponed due to the pandemic, will retrace the steps of St John Paul II, who also visited the four nations during his 27-year pontificate.

"Today I begin an Apostolic Journey to several countries in Asia and Oceania," he wrote on X on Monday. "Please pray that this journey may bear fruit."

Since his election in 2013, the Pope has urged the Catholic Church to bring God's comfort "toward the periphery" - referring to communities who are marginalised or far away.

He is only the third pope to visit Indonesia, which has the largest population of Muslims globally.

During his four days there, he is expected to visit the Indonesian capital's main mosque, meet with outgoing president Joko Widodo and hold a mass for some 70,000 people, according to the Vatican News.

Nasaruddin Umar, the grand imam at the Jakarta mosque, told news agency AP he hopes the visit will offer opportunities to "discuss the common ground between religious communities and emphasise the commonalities between religions, ethnicities, and beliefs".

Observers say the visit to Indonesia highlights the Pope's interest in deepening dialogue between Christian and Muslim communities.

"For the longest time, there [have been] tensions. [Both groups have had] misunderstandings over the course of history," said Jonathan Tan, a religious studies expert at the Case Western Reserve University in the US.

"I think what the Pope wants to do is to do a new way forward, a new way of relating to one another, not a defensive way," he said.

In Papua New Guinea, the Pope will travel to the remote city of Vanimo to meet with missionaries from his native Argentina who have been reaching out to tribal communities.

Miguel de la Calle, an Argentine missionary in Papua New Guinea's north-western-most city, said he hoped the Pope's visit would "significantly boost" ongoing evangelisation efforts in the territory.

People have been travelling from all Papua New Guinea - and even across the border from Indonesia - to see the Pope, he told Vatican News.

"Some have been walking for days due to the scarcity of transportation," Father Miguel said.

In Timor-Leste, the Pope will officiate mass in the capital Dili, on the same seaside esplanade where John Paul II spoke in 1989 to comfort local Catholics who suffered under Indonesia's occupation of the territory. Timor-Leste gained independence in 2002.

The sheen of Pope Francis's visit to the country has dimmed in recent days, however, following revelations that hundreds of homes in the area were bulldozed. Nearly 90 residents were told to find somewhere new to live before he arrives.

The Pope will wrap up his trip in Singapore, in a visit widely seen as an attempt to improve ties with China. Three-quarters of the city state's population are ethnically Chinese, and Mandarin is one of four official languages.

No pope has been able to visit China to date, as relations between the Vatican and the Chinese Communist Party have been strained by disputes over who can appoint bishops in the country.

Both sides are believed to have reached a deal on this in 2018, which gives the Vatican a say on such appointments.

For the past decade, the Pope has been increasing his engagements with Asia.

Early in his pontificate, he made four long-distance trips to the region: to South Korea, Sri Lanka, the Philippines, and Japan. Only 0.5% of Japan's population identified as Catholic at the time.

He has also visited Bangladesh, Mongolia, Myanmar, and Thailand.

During his trip, Francis will be accompanied by a doctor and two nurses. Concerns have been raised over the impact of such an ambitious itinerary on his ailing health.

Francis, who has had part of one lung removed in his younger days, had been struggling with respiratory and mobility problems of late - some of which have led him to miss his weekly Sunday blessings.

In November last year, he cancelled his trip to Dubai for the annual United Nations climate meeting because of a lung inflammation.

Additional reporting by Hanna Samosir in Jakarta