Venezuelan President Hugo Chavez has died after a two-year battle with cancer, ending the socialist leader's 14-year rule of the South American country, Vice President Nicolas Maduro has said in a televised speech.
Maduro, surrounded by other government officials, announced the death in a national television broadcast on Tuesday.
"In the immense pain of this historic tragedy that has affected our fatherland, we call on all the compatriots to be vigilant for peace, love, respect and tranquility," Maduro said.
Maduro said the government had deployed the armed forces and police "to accompany and protect our people and guarantee the peace".
"In the immense pain of this historic tragedy that has affected our fatherland, we call on all the compatriots to be vigilant for peace, love, respect and tranquility."
- Nicolas Maduro, Venezuela's vice president
Elias Jaua, the foreign minister, said Chavez's hand-picked successor Maduro would take over as interim leader pending the next election, declaring: "It is the mandate that comandante President Hugo Chavez gave us."
Venezuela's constitution, however, specifies that the speaker of the National Assembly, currently Diosdado Cabello, should assume the interim presidency if a president can't be sworn in.
Military commanders quickly pledged loyalty to Maduro.
Defence Minister Diego Molero said the armed forces would defend the constitution and respect Chavez's wishes.
The authorities said a new vote would be called within 30 days.
Chavez's body will be taken to a military academy on Wednesday, where he will lie in state until a memorial service with foreign leaders on Friday. The government has announced seven days of mourning.
Henrique Capriles, the opposition leader who lost to Chavez in October last year, said: "This is not the time for differences. This is the time for unity, the time for peace," he said, insisting he and Chavez were "adversaries, but never enemies".
Messages of condolences for Chavez's death came from around the world.
US President Barack Obama, in a statement, called Chavez's passing as a "challenging time" for Venezuela.
"The United States reaffirms its support for the Venezuelan people and its interest in developing a constructive relationship with the Venezuelan government," Obama said.
"As Venezuela begins a new chapter in its history, the United States remains committed to policies that promote democratic principles, the rule of law, and respect for human rights."
Ban Ki-Moon, the UN secretary-general, said he is "conveying condolence" to the Venezuelan president's "family and the people of Venezuela", according to Al Jazeera's James Bays, who was reporting from New York.
Vitaly Churkin, Russia's ambassador to the UN, also issued as statement describing Chavez's death as a "tragedy".
"He was a great politician for his country and for the world as a whole," Churkin said.
Meanwhile, a teary-eyed Bolivian President Evo Morales, one of Chavez's closest allies in Latin America and most loyal disciples, declared that "Chavez is more alive than ever."
"Chavez will continue to be an inspiration for all peoples who fight for their liberation," Morales said on Tuesday in a televised speech. "Chavez will always be present in all the regions of the world and all social sectors."
Al Jazeera's Gabriel Elizondo, reporting from Caracas, said "millions of people" are expected to attend the funeral.
"Chavez is known as a guy who could bring out his supporters and that is what's going to happen," Elizondo said. "He is such a big figure here in Venezuela, you cannot overstate it. He is larger than life".
Much of the capital, Caracas, was quiet overnight, with streets deserted especially in richer parts of the capital. Most shops locked their doors as the news spread, fearing looting.
Chavez easily won a new six-year term at an election in October and his death shocked millions of supporters.
"He was our father," said Nancy Jotiya, 56, in Caracas' central Plaza Bolivar. "He taught us to defend ourselves. Chavismo is not over! We are the people; we will fight!"
During more than 14 years in office, Chavez routinely challenged the status quo at home and internationally.
Chavez polarised Venezuelans with his confrontational and domineering style, yet was also a masterful communicator and strategist who tapped into Venezuelan nationalism to win broad support, particularly among the poor.
The Leftist leader repeatedly proved himself a political survivor. As an army paratroop commander, he led a failed coup in 1992, then was pardoned and elected president in 1998. He survived a coup against his own presidency in 2002 and won re-election two more times.
The burly president electrified crowds with his booming voice, often wearing the bright red of his United Socialist Party of Venezuela or the fatigues and red beret of his army days.
Before his struggle with cancer, he appeared on television almost daily, talking for hours at a time and often breaking into song of philosophical discourse.
Chavez used his country's vast oil wealth to launch social programs that include state-run food markets, new public housing, free health clinics and education programs.
Poverty declined during Chavez's presidency amid a historic boom in oil earnings, but critics said he failed to use the windfall of hundreds of billions of dollars to develop the country's economy.
Inflation soared and the homicide rate rose to among the highest in the world.
The populist leader of oil-rich Venezuela became Latin America's most vocal and controversial leader and was Washington's chief antagonist in the region.