President Tadic said Pavle's death was a "personal loss"
The head of the Serbian Orthodox Church, Patriarch Pavle, has died in Belgrade, the Church has announced.
The patriarch, 95, became leader of the Church in 1990. He was admitted to the city's military hospital two years ago.
Though he reportedly suffered from heart and lung conditions, the Church did not specify the cause of death.
Most of Serbia's population of seven million people are Orthodox Christians. President Boris Tadic said this was "an irredeemable death" for the nation.
"There are people who bond entire nations and Pavle was such a person," Mr Tadic said in a statement.
"His death is also my personal loss," the president said.
Bishop Amfilohije, who has served as acting head of the church during most of Pavle's illness, broke into tears as he held a prayer after announcing the death.
Bells tolled from Serbian churches, as the government announced three days of mourning, beginning on Monday.
Another bishop, Lavrentije, said the patriarch's death was no reason to be sad.
"The Serbian people now have someone to represent them before God better than anyone else," Lavrentije said.
The Church's highest body, the Holy Synod, may announce as early as Monday when a new patriarch will be chosen - usually after at least 40 days.
Pavle was a respected theologian and linguist, known for personal humility and modesty.
After the fall of communism and rise of Serb nationalism, the Church regained a leading role during his rule.
At the beginning of the Balkan wars that followed the dissolution of Yugoslavia in the early 1990s, Pavle said - according to Serbian state television: "It is our oath not to make a single child cry or sadden a single old woman because they are of another religion or nation."
But critics accused him of failing to contain hardline bishops and priests who supported Serb paramilitaries against Catholic Croats and Bosnian Muslims.
After those wars, Pavle became more directly involved - openly criticising Serbian President Slobodan Milosevic, after he lost Kosovo following Nato's intervention.
Since then, the Serbian Orthodox Church has strongly supported the Serbian government in its efforts to stop Kosovo's independence drive.
"Kosovo is not only a question of territory, it is a question of our spiritual being," he said after Kosovo's declaration of independence.