The Vatican says the pope died at 9:37 pm local time - 1937 Universal Time.
Vatican officials said the pontiff decided to remain at the Vatican and to not seek further hospital treatment after his health declined precipitously Thursday.
The spokesman said John Paul II developed a high fever of up to 40 degrees Celsius Thursday, as a result of a urinary tract infection that triggered septic shock - a generalized infection spreading throughout his body - and "a cardio-vascular collapse."
After intensive treatment Thursday and early Friday, however, the Vatican said the pope was "conscious, lucid and tranquil," and that he had celebrated Mass together with his aides.
The anointing of the sick, often known as the last rites or Extreme Unction, was administered to the pope late Thursday, and he also received Holy Viaticum - a special form of communion reserved for the seriously ill or dying.