Rival groups of soldiers in Burundi are vying for control of the capital Bujumbura amid confusion over the success of an attempted coup.
There has been heavy fighting at the state radio building, where broadcasts were briefly halted.
One source said soldiers loyal to President Pierre Nkurunziza controlled key areas, including the airport. Coup leaders insist they remain in charge.
The unrest began when Mr Nkurunziza announced he was seeking a third term.
Opponents say the bid contravenes the constitution.
There is no confirmation on the whereabouts of the president. Some reports say he is still in Dar es Salaam in Tanzania, where he had travelled to attend a summit.
A general supporting the coup told Agence France-Presse that troops had been ordered to take the loyalist-held state radio building with a full armoured assault.
The RTBN radio station had earlier broadcast a message from Mr Nkurunziza condemning the coup.
"I thank soldiers who are putting things in order, and I forgive any soldier who decides to surrender," he said.
But an employee there then told AFP: "We are being attacked. It is very heavy. The transmitter has been cut. We cannot transmit."
Shortly afterwards the station resumed broadcasting, initially playing music then a statement that loyalists were still in control.
"We had stopped transmitting during the attack. Now the fighting has stopped we can resume. It is still loyalist soldiers who are in control," station director Jerome Nzokirantevye said in the broadcast.
Control of the national broadcaster is key because it is the only outlet still broadcasting outside the capital, the BBC's Maud Jullien reports.
The two private radio stations have been shut down. The most popular - Radio Publique Africaine - was burnt down overnight after broadcasting Gen Niyobare's coup announcement.
A senior military source earlier told BBC Afrique that loyalist troops were in control of the presidential palace, the radio station, the airport and the centre of Bujumbura.
Both army chief of staff Gen Prime Niyongabo and President Nkurunziza said the coup attempt had been halted.
But this has been contradicted by the coup leaders, one of whom said they were in control of "virtually the entire city" of Bujumbura.
"The soldiers who are being deployed are on our side," coup spokesman Venon Ndabaneze told AFP.
BBC correspondents say the streets seem to be mainly in the control of loyalist police, and the airport has reportedly reopened, which would appear to confirm reports it too is in loyalist hands.
At the scene: Ruth Nesoba in Bujumbura
Sporadic gunfire is still being heard in parts of Bujumbura and many business premises have remained closed this morning.
Roads have been barricaded and only a few vehicles are on the empty streets, mainly emergency service vehicles attending to those injured in the on-and-off shooting.
In one neighbourhood, the BBC saw angry crowds of young men asking police on patrol to leave. The men, most of them casual labourers, said they had been unable to make it to work because of restrictions on their movements.
Commodities are running out. Petrol has become scarce and where it is in stock there are long queues.
The coup was announced by Maj Gen Godefroid Niyombare, a former intelligence chief and ally of the president, on Wednesday.
"The masses vigorously and tenaciously reject President Nkurunziza's third-term mandate. President Pierre Nkurunziza has been relieved of his duties," he said in a radio broadcast.
Thousands of people took to the streets to celebrate, marching on the centre of Bujumbura alongside soldiers.
Gen Niyombare made the announcement hours after the president flew to Dar es Salaam to discuss the crisis with regional leaders.
He reportedly tried to fly back to Burundi upon learning of the coup attempt, but had to return to Dar es Salaam as the airport at Bujumbura was closed.
President Nkurunziza's fellow leaders at the summit condemned the coup.
The unrest began on 26 April after the 51-year-old president said he would run for re-election in June.
He argued that he was entitled to a third term because he was first appointed to the role by parliament in 2005, rather than be elected.
The constitution states a president can only be elected to two terms in office, but earlier this month the country's constitutional court upheld Mr Nkurunziza's interpretation.
More than 20 people have died and tens of thousands of Burundians have fled to neighbouring states since the unrest began.