Zambia's government on Wednesday announced that President Michael Sata, 77, has died in London, where he was receiving medical treatment.
"It is with a heavy heart that I announce the passing on of our beloved president," government cabinet secretary Roland Msiska said.
Msiska said Sata died in London's King Edward VII hospital, and called for Zambians to remain calm.
Sata has long been rumoured to be seriously ill and had not been seen in public since returning from the UN General Assembly last month, where he failed to make a scheduled speech.
He flew to London just over a week ago for treatment.
Sata made a rare public appearance on September 19 to tell parliament: "I am not dead."
When he left Zambia for London, Sata appointed Minister of Defence and Justice Edgar Lungu as acting president.
Despite repeated denials that the president was ill, analysts had said a power struggle was already under way behind the scenes for Zambia's top job.
Supporters who voted Sata into office in 2011 saw him as a no-nonsense man of action, while for critics, the former policeman, trade unionist and taxidermist was an authoritarian populist.
What is undisputed is that he seemed to revel in scorched earth politics.
Detractors, political foes, the media and even allies frequently came under attack from a man who earned the sobriquet "King Cobra".
He had recently cracked down on political opponents and critical journalists who reported on his long-suspected illness and frequent "working trips" abroad, apparently for medical treatment.
In January 2014, an opposition politician was charged with defamation for calling him a potato, while in June the authorities charged three opposition activists for claiming that he was dying.
