ROME (REUTERS) - Pope Francis will celebrate a landmark birthday this weekend.

He's turning 80 on Saturday (Dec 17).

In keeping with the pontiff's low-key style, no special events have been organised - but the Vatican is commemorating the milestone with a special stamp.

"This special issue for a pope who turns 80 is typical practice for the Vatican. We have done this for Paul VI, for John Paul II, for Pope Ratzinger," said Vatican Philatelic and Numismatic Office's Mauro Olivieri.

A Spanish artist was commissioned to paint the picture used for the stamp, which also represents the Pope's homeland of Argentina.

The booklet containing the four stamps is on sale for US$20 (S$28), and can be bought or ordered from the Vatican post office.

"Pope Francis is a pope who is very loved. The public, collectors, pilgrims and the faithful and tourists in St. Peter's square all ask for images of the pope. This is an image we have worked on, it is a painting and it is very affective, it is beautiful and colourful and it is a great image of the pope so I imagine this will, as usual, be greatly requested," Mr Olivieri said.

Pope Francis was born in Buenos Aires in 1936.

He is the first non-European pope in more than a thousand years, and the first ever from Latin America.