The pontiff's condition is touch-and-go, given his age, fragility and pre-existing lung disease, according to doctors.

The kidney ailment appears to be in an early stage, the Vatican said, adding that the pontiff is still receiving high flows of oxygen for his respiratory illness.

Officials said Pope Francis is in critical condition as he battles pneumonia and early kidney failure. He was awake and eating normally during his treatments. Crowds have been gathering at Vatican City to pray for his recovery. Doctors reported Sunday that blood tests showed his early kidney failure was under control.