Pope Francis is being kept in hospital for checks after attending a scheduled appointment at a hospital in Rome, Vatican sources say.
The pontiff’s closest staff, including security, are expected to stay the night at the Gemelli Hospital, a person with direct knowledge of the matter told the BBC.
Pope Francis’ schedule has reportedly been cancelled for the next two days.
A source said medical checks would continue for as long as necessary.
It is not clear whether a new ailment prompted his visit to hospital.
This is the busiest time of the year for Pope Francis, 86, with many events and services scheduled ahead of Palm Sunday and Easter weekend.
In January, the Pope led the funeral of his predecessor Pope Benedict XVI – who was the first pope to resign due to ill health for centuries.
Pope Francis has previously indicated that he may also wish to follow in Benedict’s footsteps in the event that his health deteriorated.