Pope Francis has suspended the use of an oxygen mask, the Vatican said on Wednesday, adding that the 88-year-old's clinical conditions were "improving" after more than one month in hospital.

The Argentine pope has been in Rome's Gemelli hospital since February 14 suffering from pneumonia in both lungs, but the Vatican has reported recent progress after earlier worries that his life could be at risk.

"The Holy Father's clinical conditions are confirmed to be improving," wrote the Vatican in a medical bulletin, which it is now publishing only sporadically, instead of daily, due to his improved health.

He has "suspended non-invasive mechanical ventilation and also reduced the need for high-flow oxygen therapy", it said, adding that there was progress in the pope's motor and respiratory physiotherapy.

After a series of breathing attacks earlier in the pope's hospital stay, his breathing has improved over the past week, with the Vatican on Monday saying he was spending short moments breathing on his own.

During the day he has relied on a cannula -- a plastic tube tucked into his nostrils -- to deliver high-flow oxygen, which doctors are now reducing.

Until this week, Francis had worn an oxygen mask but on Tuesday the Vatican said he had managed without one for the first time.

Francis is prone to respiratory illnesses and had part of one lung removed as a young man.

Despite his recent improvements, the Vatican has yet to say when he could be released from the hospital.

At the weekend, it said the Jesuit still required therapies to be administered from the hospital.