Pope Francis's health is improving after spending a night in hospital with a respiratory infection, the Vatican announced on Thursday, saying the 86-year-old had eaten breakfast, read the newspapers and even done some work.

The pope "rested well during the night. His clinical picture is gradually improving and he is continuing his planned treatment", spokesman Matteo Bruni said in a statement.

"This morning after breakfast, he read some newspapers and resumed work. Before lunch, he went to the little chapel of the private (hospital) apartment where he prayed and he received the Eucharist."

Pope Francis was admitted to Rome's Gemelli hospital on Wednesday for what the Vatican said were pre-planned checks.

It later revealed he had complained of breathing difficulties and was diagnosed with a respiratory infection, but not Covid, and required "a few days" of hospital treatment.

The Argentine pontiff, who earlier this month marked 10 years as head of the Catholic Church, has suffered a number of health issues throughout his life, including having part of one of his lungs removed at age 21.

While keeping a busy schedule and travelling widely, he has for the past year used a wheelchair due to knee pain, and admitted last summer he had to slow down.

His admission to hospital sparked widespread concern, particularly after unconfirmed reports that he arrived in an ambulance.

Francis was forced to cancel Thursday's engagements, and there are now questions over his presence at services for the upcoming Holy Week and Easter, the most important period in the Christian calendar.

Preparations are already under way at the Vatican for this weekend's Palm Sunday celebrations.

At his weekly audience on Wednesday morning, just hours before his admission to hospital, the pope appeared in good spirits, smiling as he greeted the faithful from his "popemobile".

But he was pictured grimacing as he was helped getting onto the vehicle – a photo that made all the major front pages of Italy's newspapers on Thursday. (AFP)