Pope Francis will visit Venice on Sunday, his first trip outside Rome in seven months, which will be closely watched amid concerns over the 87-year-old's fragile health.

The Argentine pontiff has toured the world in his 11 years as head of the Catholic Church, but has not travelled since visiting the French city of Marseille in September.

He was forced to cancel a trip to Dubai in December, where he was to have addressed UN climate talks, due to a bout of bronchitis.

And he pulled out of an Easter event at the last minute in March, after suffering for several weeks from what the Vatican called a "light flu".

In Venice, the pope's first stop will be a women's prison on the island of Giudecca, which houses the Vatican's entry for this year's Biennale festival of art.

At the former convent which now houses long-term prisoners, Francis -- who has long championed the rights of marginalised people -- will meet with some of the 80 inmates and visit the exhibition.

An immersive art show, "With my Eyes" considers the daily lives of the prisoners through the work of 10 different artists.

"It will be a historic moment because he will be the first pope to visit the Venice Biennale," said the exhibition's lead curator, Jose Tolentino de Mendonca.

The visit "clearly demonstrates the desire of the Church to consolidate a fruitful and close dialogue with the world of art and culture".

Mass on St. Mark's Square

Chiara Parisi, who also worked as a curator on the project, told AFP the prisoners were awaiting the visit with "huge wonder" and "hope".

"By going there to be among them, the pope's actions speak louder than words," highlighting a section of society "who are keen to play a role even when they are in a very difficult situation", she said.

Francis is due to arrive by helicopter on Giudecca at 8:00 am (0600 GMT).

After visiting the prison, he will give a speech and meet young people at the Basilica di Santa Maria della Salute, a landmark church on the south end of the Grand Canal.

From there the pope will head to St Mark's Square via a bridge built on a base of boats lined up across the canal and preside over a mass starting at 11 am.

He is due to leave Venice at 1 pm, after becoming the fourth pope to visit the city, after Paul VI (1972), Jean-Paul II (1985) and Benedict XVI (2011).

The diocese of Venice is one of the largest in Italy, with 125 parishes, and has close ties with the papacy. Three Venice patriarchs became popes in the 20th century.

Francis's visit comes on the same weekend as Venice launches a new entry fee for day-trippers, aimed at easing the pressure of tourism on the UNESCO World Heritage site.

As a guest, he will be exempt from buying a five-euro ($5.30) ticket, but non-resident pilgrims visiting for his mass will have to pay.

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.

Despite his health, the Vatican is planning an ambitious trip to Asia in September, taking in Indonesia, Papua New Guinea, East Timor and Singapore over 12 days.

Before that, the pope is due to make two other trips within Italy, to Verona in May and Trieste in July.