A group of military officers say they have seized control of Guinea-Bissau amid reports that the president, Umaro Sissoco Embaló, has been arrested.
Shortly after gunshots were heard in the capital, Bissau, government sources told the BBC that Embaló had been detained.
The officers then appeared on state TV, saying they had suspended the electoral process, as the West African nation awaited the outcome of Sunday's presidential election.
They said they were acting to thwart a plot by unnamed politicians who had the support of a well-known drug baron to destabilize the country, and announced the closure of its borders and imposed a night-time curfew.
Sandwiched between Senegal and Guinea, the coup-prone country is known as a notorious drug-trafficking hub where the military has been influential since independence from Portugal in 1974.
The election results were expected on Thursday - both Embaló and his closest rival Fernando Dias had claimed victory.
Late on Wednesday afternoon, Embaló told France 24 in a phone call: I have been deposed. Government sources have since told the BBC that Dias, Pereira and Interior Minister Botché Candé have also been detained.
The putschists have taken army chief Gen Biague Na Ntan and his deputy, Gen Mamadou Touré, into custody too, the sources say.
Checkpoints have been erected across Bissau and the streets were deserted ahead of the curfew, starting at 19:00 GMT. Portugal has called for a return to constitutional order, urging all involved to avoid any acts of violence.
Embaló has said he has survived multiple coup attempts during his time in office but is criticized for allegedly fabricating crises to clamp down on dissent. Guinea-Bissau, one of the poorest countries globally, has seen at least nine coups or attempted coups in the past five decades.
