Eyadema - who claimed sole control in 1967 after aiding what was sub-Saharan Africa's first post-colonial coup four years earlier - suffered a heart attack in his southeastern hometown of Piya early on Saturday and died on the way to Europe for treatment, officials said.
Hours later, Togo's military high command said Eyadema's 39-year-old son, Faure Gnassingbe, was the West African nation's new president.
State television showed military leaders, including army Chief of Defence Staff General Zakari Nandja, swearing an oath of allegiance to Gnassingbe, who was the minister of mines and communication.
Law and order
Prime Minister Koffi Sama called upon security forces to keep law and order. He announced all borders and air space in the nation of 5.5 million people had been closed, along with the international airport in the capital, Lome.
"The armed forces and police must help preserve peace and national security," Sama said on state radio. "All the country's political, social, religious leaders must avoid any act likely to plunge the country into anarchy and confusion."
"All the country's political, social, religious leaders must avoid any act likely to plunge the country into anarchy and confusion"
Togo's constitution calls for the speaker of parliament to succeed the president in the event of his death. By law, the speaker must call national elections to choose a new president within 60 days.
Nandja, however, said the speaker of parliament, Fanbare Tchaba, was out of the country and the military had declared Eyadema's son president to insure stability. Nandja did not say whether the move was temporary.
"The armed forces of Togo finds itself faced with the evidence of a total vacuum of power in Togo. This is because the speaker of the national assembly is absent," Nandja said. "Therefore, in order not to create a power vacuum, the armed forces of Togo has decided to declare Faure Gnassingbe the head of state."
It was also reported that the speaker arrived in neighbouring Benin late on Saturday after his plane was unable to land in Lome, an airport source in Benin said.
Nigeria's President Olusegun Obasanjo, chairman of the African Union (AU), branded as unconstitutional the army's appointment of Gnassingbe on Saturday.
Washington encouraged Togo to
"President Obasanjo will not accept any unconstitutional transition of power in Togo," said the Nigerian president's spokeswoman, Remi Oyo.
"Speaking on behalf of the AU, President Obasanjo has urged the people of Togo to insist on respect of the constitution on the provision of an interim leadership that will lead to the
democratic election of a new president for Togo," she said.
AU Commission President and a former president of Mali, Alpha Omar Konare, said it was a military coup.
"What is happening now in Togo, you must call things by their proper name, is a seizing of power by the army. It's a military coup d'etat," he said.
Last of a kind
Eyadema, a former Togolese French Foreign Legion officer, had survived assassination attempts, international isolation over rights abuses and uprisings.
He was considered one of Africa's last "big men" - rulers holding power through patronage, the loyalty of their ethnic and regional groups, and military force.
Elections that returned Eyadema to power in 2003 were internationally criticised.
The European Union imposed sanctions on Togo in 1993 after allegations that security forces opened fire on democracy activists, killing about 20 people. International rights organisations accuse his government of suppressing the opposition and charged him with widespread rights abuses. Most aid to the tiny country remains frozen.
Annan: Eyadema contributed to
settling disputes in Africa
In more recent years, perhaps in an effort to rehabilitate his image, Eyadema took part in regional efforts to bring peace to Burundi, Ivory Coast and Liberia.
UN Secretary-General Kofi Annan expressed his deep sorrow for the president's death, according to a statement from his office, saying Eyadema had "made a significant contribution to the peaceful settlement of disputes in Africa in general and in West Africa in particular".
Eyadema was believed to have heart problems, but the state of his health was not made public. Two weeks ago, he travelled to Switzerland for what authorities said was a medical checkup.