The military says it has seized power in oil-rich Gabon, where the ailing leader's family has ruled for 50 years.
Soldiers in the west African country say they launched a coup "to restore democracy".
They took control of the national radio station at 04:00 local time (03:00 GMT) to read a short statement announcing a "National Restoration Council".
President Ali Bongo took over power in 2009 and has been out of the country for more than two months.
Tanks and armed vehicles can be seen on the streets of the capital Libreville.
President Bongo reportedly suffered a stroke in October and received treatment in Morocco.