Soldiers have taken control of much of the capital of the Guinea-Bissau in what appears to be a coup attempt.
Heavy gunfire was heard in the city of Bissau and at the residence of outgoing Prime Minister Carlos Gomes Junior.
Troops also took control of the national radio station and ruling party's headquarters.
Mr Gomes came first in an inconclusive presidential election last month, but failed to win outright. His whereabouts are not known.
West African regional organisation Ecowas condemned what it described as an attempted coup.
"I personally saw some military vehicles close to the residence of the prime minister, and 20 minutes later, we heard an explosion, probably an RPG [rocket propelled grenade], and then shooting sounds. We heard this not on a regular basis, but we heard this shooting for one hour," a Bissau resident, who wished to remain anonymous, told the BBC about events on Thursday night.
The whereabouts of the interim president, Raimundo Pereira, is also unknown, reports say.
By Friday morning another resident told the BBC that state television and radio were still off air and there had been no message from the military.
But people had started to go out on to the streets, where there was no longer a presence of soldiers, she said.
Ivory Coast's Foreign Minister Daniel Kablan Duncan said Ecowas would not tolerate the actions of the military.
Ecowas has recently intervened in Mali, where there was a coup last month, ordering the coup leader to hand over power after imposing sanctions.
"It's sad that after the example of Senegal, where the elections finished so well, that we have, after Mali, a new forceful intervention in Guinea-Bissau," Mr Duncan told the BBC's Network Africa programme.
"What I can say at this moment is that... the situation won't be accepted by Ecowas," he said.
Last month's emergency vote was called after the death in January of President Malam Bacai Sanha following a long illness.
The second-placed candidate in the March election, former President Kumba Yala, has said he will boycott the run-off vote scheduled for 29 April. He alleged that the election had been fraudulent.
Guinea-Bissau, an impoverished former Portuguese colony, has been plagued by a long series of coups since gaining independence in 1974.
It has recently become an important staging post for gangs smuggling drugs from Latin America to Europe.