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 capital city Bissau, government sources told the BBC that Embaló had been detained.
The reports come three days after a presidential election in which the main opposition candidate was disqualified.
The results were expected on Thursday - both Embaló and his closest rival Fernando Dias have claimed victory.
Witnesses in Bissau heard gunfire at around 13:00 GMT on Wednesday but it was not immediately clear who was involved in the shooting or if there were any casualties.
Hundreds of people on foot and in vehicles fled, seeking shelter as the shots rang out, the AFP news agency reported.
Later on, army officers made an address on state TV, saying they had formed "the High Military Command for the Restoration of Order" and would be in charge of the West African nation until further notice.
The soldiers instructed the population to "remain calm".
Guinea-Bissau, with a population of just under two million people, is one of the poorest countries in the world. The former Portuguese colony has seen nine coups or attempted coups since 1980.
There have been two attempts to overthrow Embalo, the latest in December 2023.