Three days of national mourning are to be held for ex-President Luis Cabral
The first post-independence President of Guinea-Bissau, Luis Cabral, has died in Portugal's capital, Lisbon, aged 78.
Mr Cabral was president from 1974 until 1980 when he was overthrown by his prime minister, Joao Bernardo Vieira, who was assassinated three months ago.
Mr Cabral was a half-brother of the liberation movement leader, Amilcar Cabral, who died before independence.
The government is expected to hold an emergency session to organise a three-day period of national mourning.
"It is with shock and sadness that the government and people of Guinea-Bissau have learnt of the loss of one of their most illustrious sons, Luis Cabral," the government said in a statement, reported AFP news agency.
The BBC's Tidiane Sy, in neighbouring Senegal, says it is ironic that the ex-Guinean leader is now being mourned by the country which rejected him nearly three decades ago.
His half-brother - who led the African Party of Independence of Guinea and Cape Verde movement - was assassinated in 1973.
Mr Cabral then took over as leader of the liberation struggle and brought the country to independence from Portugal a year later.
He was described by his fellow comrades during the liberation struggle as an eternally "optimistic and enthusiastic leader".
Mr Cabral was also remembered as a man who contributed much to the education of the masses during the first years after independence.
But our correspondent says his effectiveness as head of state was weakened by widespread hunger in the country in the late 1970s.
These hard times culminated with the November 1980 military coup which ousted Mr Cabral.
It opened a crippling era of military insurgencies, coups and counter coups for Guinea-Bissau.
After his overthrow, Mr Cabral was jailed for six months before being released following the intervention of the Cuban government.
The former Guinean president then spent some time in exile in Cuba, before settling in Lisbon in 1984.
Mr Cabral refused to make any public criticism against his former prime minister who had chased him from power.
Mr Vieira, who won elections in 2005, met a bloody end in March when he was assassinated by soldiers.