Pope Francis will visit Indonesia, Papua New Guinea, East Timor and Singapore in September, the Vatican announced Friday, an ambitious trip that could test the 87-year-old's increasingly fragile health.

Running from 2 to 13 September, the trip covering around 30,000 kilometres (18,600 miles) in total is the longest for the Argentine since he became head of the worldwide Catholic Church in 2013.

"He will visit Jakarta from 3 to 6 September, Port Moresby and Vanimo from 6 to 9 September, Dili from 9 to 11 September and Singapore from 11 to 13 September," the Vatican said in a statement.

The visit has been on the cards for months, but the pontiff's health issues had raised questions on whether it would go ahead. 

Francis pulled out of a key Easter event at the last minute at the end of March, and has asked aides to read several of his speeches in recent weeks due a bout of bronchitis.

The pontiff, who uses a wheelchair, has suffered increasing health problems in recent years, from knee pain to surgery for a hernia and on his colon.

He is known for his work ethic -- he never takes holidays -- but has been forced to make concessions to his age and health, including cancelling a trip to UN climate talks in Dubai last year.

Involving more than 30 hours of flight, an eight-hour time difference and a series of meetings and masses, the September trip will represent a major physical challenge.

Francis had been due to visit Papua New Guinea, East Timor and Indonesia in September 2020 but the trip was cancelled because of the coronavirus pandemic.

The government in Indonesia, which has the world's largest Muslim population, had already announced the pope's visit last month, describing it as a "special gift" for the country's Catholics.

In a statement Friday, its foreign ministry said the visit was important "for all religious communities".

"The visit is also expected to strengthen the message of tolerance, unity and world peace."