Heavy gunfire has been heard in the centre of Guinea's capital, Conakry, while soldiers have been seen on the streets near the presidential palace.
The reason for the shooting is not clear, and authorities in the West African country have not commented.
The district of Kaloum is reported to be deserted as terrified residents heed soldiers' orders to stay at home.
A senior government official told Reuters that President Alpha Conde was unharmed but gave no further details.
The only bridge connecting the mainland to the Kaloum peninsular, which houses most ministries and the presidential palace, had been sealed off and many soldiers, some heavily armed, were posted around the palace, a military source told Reuters.
There are unconfirmed reports that three soldiers have been killed.
- QUICK GUIDE: Guinea country profile