Raul Castro made the announcement just after midnight Friday (0500 GMT Saturday).
Havana plunged into mourning Saturday and celebrations erupted in Miami at the death of Cuban revolutionary leader Fidel Castro, whose iron-fisted rule defied the United States for a half century.
One of the world's longest-serving rulers and among modern history's most striking personalities, Castro died Friday night at age 90 after surviving 11 US administrations and hundreds of assassination attempts.
Castro crushed opposition at home from the moment he took power in 1959 to the day he handed over to his younger brother Raul in 2006 amid a health crisis.
For defenders of the revolution, he was a hero who protected ordinary people from capitalist domination.
To opponents, including thousands of Cuban exiles living in the United States, he was a cruel communist tyrant.
After surviving the failed Bay of Pigs invasion, the Cuban Missile Crisis, a suffocating US embargo and the Cold War itself, Castro lived to see the restoration of diplomatic ties with Washington last year.
But he never stopped railing against the American "empire."
President Raul Castro announced the news on national television. He gave no details on the cause of death.
There were starkly different reactions on either side of the Florida Straits.
In the streets of Miami, home to the largest Cuban-American community, euphoric crowds waved flags and danced, banging pots and drums.
"It's sad that one finds joy in the death of a person -- but that person should never have been born," said Pablo Arencibia, 67, a teacher who fled Cuba 20 years ago.
"Satan is now the one who has to worry," he added, because "Fidel is heading there and is going to try to get his job."
In Havana, bustling streets emptied and Friday night parties ground to a halt as Castro's admirers sank into grief.
"Losing Fidel is like losing a father -- the guide, the beacon of this revolution," said Michel Rodriguez, a 42-year-old baker.
Castro was to be cremated Saturday, the first of nine days of mourning.
A series of memorials will begin Monday morning, when Cubans are called to converge on Havana's iconic Revolution Square.
Castro's ashes will then go on a four-day procession through the country, before being buried in the southeastern city of Santiago on December 4.
Castro's death drew strong -- and polarized -- reactions across the world.
"The name of this distinguished statesman is rightly considered the symbol of an era in modern world history," said Russian President Vladimir Putin in a telegram to Raul Castro.
"Comrade Castro will live forever," said Chinese President Xi Jinping in a message read on television. "History and people will remember him."
North Korean leader Kim Jong-Un sent his condolences and praised Castro as an "outstanding leader" who fought to make the people "the genuine masters for the first time in the Western hemisphere."
Venezuela, Cuba's main ally in the region, declared three days of national mourning. In a rally Saturday night outside the tomb of Hugo Chavez, the leftist leader who was a staunch ally and good friend of Castro, President Nicolas Maduro said, "Fidel, go in peace, because we are still here." Some in the crowd wept.
In the US, there were sharply different reactions from outgoing President Barack Obama and President-elect Donald Trump.
Obama, who embarked on a historic rapprochement with Cuba in 2014, said the US extended a "hand of friendship" to the Cuban people.
But Trump called Castro "a brutal dictator who oppressed his own people for nearly six decades."
The future of the US-Cuban thaw looks uncertain under Trump.
He has threatened to reverse course if Cuba does not allow greater human rights.
Cuba says it refuses to be dictated to by foreign powers.
Fidel Castro came to power in 1959 as a black-bearded, cigar-chomping 32-year-old, in a revolution against dictator Fulgencio Batista.
"When this war is over, a much longer greater war will begin: the war that I am going to wage against them," he said in 1958, referring to the United States.
"That will be my true destiny."
Living by the slogan "socialism or death," he kept the faith to the end.
He endured more than 600 assassination attempts, according to aides, and the disastrous US-backed Bay of Pigs invasion attempt in 1961.
His outrage over that botched plot contributed to the Cuban Missile Crisis in 1962, when the Soviet Union agreed to his request to send ballistic missiles to Cuba.
The US discovery of the missiles pushed the world to the brink of nuclear war.
"If I am considered a myth, the United States deserves the credit," Castro said in 1988.
Born August 13, 1926 to a prosperous Spanish immigrant landowner and a Cuban mother of humble background, Castro was said to be a quick learner and a keen baseball player.
Defending himself at his trial, the trained lawyer said defiantly: "History will absolve me."
After serving two years in prison then going into exile in Mexico, he set sail for Cuba on December 2, 1956 with a band of rebels on the yacht Granma.
Twenty-five months later, they ousted Batista and Castro was named prime minister.
He threw Cuba's lot in with the Soviet Union, which bankrolled his regime until 1989, when the Eastern Bloc's collapse sent Cuba's economy plunging.
Still, Fidel managed to hang on.
He ceded power to Raul, now 85, in July 2006 to undergo intestinal surgery.
He faded from public view, but continued publishing diatribes in the state press and wielding influence behind the scenes.
Castro fathered seven children with three women, two of whom he married.
He was last seen in public on his 90th birthday on August 13.