Pope Francis, who is receiving treatment for a respiratory tract infection, had a peaceful night in Rome's Gemelli hospital, Italian media reported on Sunday, while a senior cardinal led a prayer for his recovery.

Francis, 88, will not appear in public on Sunday to deliver his usual weekly prayer with pilgrims because he has been told to rest.

The pontiff has been suffering from bronchitis for more than a week and was admitted to hospital on Friday morning.

"Our first thought goes to Pope Francis. We pray for his health, offering thanks for the vision and support that he always gives us," Cardinal Jose Tolentino de Mendonca said during a mass in St Peter's Basilica on Sunday.

The cardinal was leading the mass, dedicated to honouring artists in the Catholic Church's Holy Year, in the absence of Francis.

A Vatican statement released late on Saturday said that the pope had been "prescribed complete rest" in order to help his recovery.

The pope's treatment on Saturday was "slightly modified based on further microbiological findings", the statement said. "Today's laboratory tests showed an improvement in some values," it added.

Francis briefly watched some of the main evening news bulletin on Italy's RAI TV at 8 p.m. (1900 GMT) on Saturday before having a restful night, Italy's ANSA news agency reported.

The Vatican has said the pope would remain in hospital as long as necessary for his treatment.

Francis, who has been pontiff since 2013, has had influenza and other health problems several times over the past two years.