The Pope died in his private apartment at the Vatican at 2137 local time (1937 GMT) on Saturday, surrounded by his closest Polish aides.
Many thousands of people gathered in Rome's St Peter's Square to pay tribute to the pontiff, while church bells throughout the city began tolling.
The Pope had suffered worsening health problems including a heart condition.
Our Holy Father John Paul has returned to the house of the Father
Archbishop Leonardo Sandri
Senior Vatican official
Watch the statement
The Pope then received the Viaticum, a Catholic rite for the sick and dying.
Long applause
The Italian government has declared three days of mourning.
News of the Pope's death was received with intense emotion
The funeral date has not been set but it is not expected before Wednesday.
Pope John Paul II died after suffering from heart and kidney problems and unstable blood pressure.
Minutes after his death, the Vatican issued a brief statement to confirm the news, adding that procedures to be carried out in the event of the death of the Pope had been set in motion.
THE POPE'S LIFE 1920 - Born near Krakow, Poland 1964 - Archbishop of Krakow 1978 - Elected first non-Italian Pope for 450 years 1981 - Assassination attempt 2002 - Final visit to homeland
Obituary: John Paul II
The news was met with long applause, an Italian sign of respect, followed by several minutes of silence as the crowd took in the news.
"Our Holy Father John Paul has returned to the house of the Father," senior Vatican official Archbishop Leonardo Sandri said.
The BBC's Peter Gould, at the Vatican, says people in the square stood in groups, comforting one other.
In the Pope's native Poland, people fell to their knees and wept as the news reached them.
Tributes have been coming in from political and religious leaders in other parts of the world.
US President George W Bush said the world had lost a champion of freedom.
YOUR TRIBUTES A wonderful beacon of truth and justice for the world
John O'Byrne, Dublin, Ireland
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The Cardinal Chamberlain of the Roman Catholic Church, Eduardo Martinez Somalo, is now in charge.
He has to seal the papal apartments and summon the cardinals from around the world to elect the Pope's successor.
The cardinals, many of whom are already on their way to Rome, must meet no more than 20 days after the Pope's death to choose a successor. A preliminary meeting has been arranged for Monday morning.
Breathing trouble
The Pope's condition deteriorated suddenly on Thursday night with a high fever caused by an infection of the urinary tract.
He had been suffering from breathing troubles, exacerbated by the progress of Parkinson's Disease, an incurable condition from which he had been suffering for nearly a decade.
He appeared briefly at the window of his Vatican apartment on Easter Sunday to bless the faithful, but was unable to speak.
It was the first time during his 26-year pontificate that the Pope had delegated the main Easter ceremonies to his cardinals.
Polish-born Karol Wojtyla became Pope in 1978, taking a conservative stand on issues like abortion and contraception.
He was the most widely travelled pontiff and visited more than 120 countries during his 26-year papacy.
Stock image of Pope John Paul II in the Vatican
'''John Paul II (Karol Józef Wojtyła) 1920-2005'''

After months of failing health, ''His Holiness'' Pope John Paul II passed away today, April 2, at 9:37 p.m. local time (19:37 UTC). He was 84 years old.  An email message to journalists from the spokesman Joaquin Navarro-Valls from The Vatican confirmed the death at 20:00 UTC.

The Pope had a  earlier this year to help him breathe, and then lost his ability to speak last week. On Thursday March 31 he developed a urinary tract infection that led to septic shock and cardiovascular collapse.  A nasogastric feeding tube was inserted to help him regain strength.  The Pope elected not to return to Rome's Gemelli hospital, but instead to stay in his own apartments where he was tended to by his personal doctors and Vatican medical staff.

The same night, he was administered the '''' also known as the last rites. On Friday April 1, the Vatican said he was having difficulties with both his heart and his kidneys.

 news agency Agenzia Giornalistica Italia reports the pope's final message was "I am happy, you be happy, too. Let's pray together with joy. I entrust everything to the Virgin Mary with joy".

A description of the last moment of the holy father from father Jarek Cielecki, director of the Vatican service news and of the Italian TV catolic Tele Padre Pio, tells us the last moment of life of this great man. "The Holy father died looking at the window, gathered in prayer. As such he was conscious. Just before dying, the Pope raised his right hand in a sign of blessing, as if he was aware of all the people gathered in prayer. Then, as soon as the prayer ended, the Pope did a huge effort, said the word 'Amen' and died."

The Vatican has announced that the funeral will take place on Wednesday, April 6 and that the Pope's body will lie in state from Monday, April 4.