Reports from Bissau, the capital of the West African nation of Guinea-Bissau, say there has been gunfire in the vicinity of the presidential palace.
Reports say soldiers have surrounded the building. President Umaro Sissoco Embaló is understood to be inside.
A witness in Guinea-Bissau has told BBC Focus on Africa that armed men in civilian clothing opened fire at the ministerial palace in the capital, Bissau, where the president and prime minister were holding a meeting.
The current whereabouts of President Umaro Sissoco Embaló and Prime Minister Nuno Gomes Nabiam are unknown, the source says.
According to the witness, the military and police went to the scene where the armed men were firing, following which a police officer was shot.Soldiers are patrolling the streets of Bissau in military vehicles and some calm has returned.
Guinea-Bissau has a long history of political instability and military coups, the last of which was in 2012.