Pope Francis conscious and receiving supplemental oxygen, the Vatican says

Pope Francis is conscious and still receiving high flows of supplemental oxygen following a respiratory crisis and blood transfusions as he remains in critical condition with a complex lung infection, the Vatican has said.

"The night passed quietly, the pope rested," Vatican spokesman Matteo Bruni said in a statement.

Further clinical tests were being performed on the 88-year-old pontiff who had part of one lung removed as a young man.

On Saturday, Pope Francis suffered a prolonged asthmatic respiratory crisis that required "high flows" of oxygen to help him breathe through a nasal tube.

He also received blood transfusions after tests showed low counts of platelets, which are needed for clotting, the Vatican said.

Doctors said that his prognosis was "reserved."

Doctors have said Pope Francis' condition is touch-and-go, given his age, fragility and pre-existing lung disease.

His condition has revived speculation about what might happen if he becomes unconscious or otherwise incapacitated and whether he might resign.

Francis was supposed to have celebrated Mass on Sunday morning in St. Peter's Basilica and ordained deacons as part of the Vatican's yearlong Holy Year commemoration.

The organiser of the Holy Year, Archbishop Rino Fisichella, celebrated the Mass in his place and offered a special prayer for the Pope from the altar before delivering the homily the pope had prepared.

"Even though he is in a hospital bed, we feel Pope Francis close to us, we feel him present among us," Fisichella told the hundreds of assembled deacons.

A pre-written message that Pope Francis had prepared for his Sunday noon prayer said he was "confidently continuing my hospitalisation at the Gemelli Hospital, carrying on with the necessary treatment; and