A marked improvement in Pope Francis' health was seen on Thursday, the Vatican said the day after the pontiff was hospitalized with breathing difficulties, and he could leave hospital in "the coming days".

Citing the medical team at Rome's Gemelli Hospital, the Vatican said in a statement that Francis received antibiotic infusion treatment for bronchitis and has since felt significantly better.

The 86-year-old pope spent Thursday afternoon "resting, praying and working a little," the Vatican added.

Earlier, Italian news agency ANSA reported that medical staff were "very optimistic" and believed the pope could be discharged from hospital in time for the Palm Sunday celebrations on April 2.

It is not immediately known if François would be able to participate in the various services if he were indeed to leave the hospital by this weekend.

Palm Sunday marks the start of an intense week of ceremonies leading up to Easter Sunday, April 9, the holiest day in the Christian calendar.

Francis, ruler of some 1.4 billion Catholics around the world and who this month celebrated his tenth anniversary of pontificate, is sometimes out of breath and generally more prone to respiratory problems. He had part of a lung removed in his early twenties.

Pope Francis' health has come under increased scrutiny over the past two years, during which he had colon surgery and started using a wheelchair or cane due to chronic knee pain.

His latest hospitalization has revived speculation about a possible resignation for health reasons, as his late predecessor Benedict XVI had done.