At least 30 commercial ships dropped anchor on Wednesday around Gabon's waters after military officers said they had seized power in the Central African country, according to data and maritime sources.
Military officers in oil-producing Gabon said they had put President Ali Bongo under house arrest, after the country's election body announced that he had won a third term. Borders were closed and state institutions were dissolved.
There was already a build-up of vessels backed up on Wednesday.
The vessels included commercial cargo ships as well as tankers and had stopped near to the country's major ports including Owendo, near to the capital Libreville, and Port Gentil further south, ship tracking data from analytics company MarineTraffic showed on Wednesday.
British maritime security company Ambrey said port operations in Libreville had stopped and no vessels had entered or departed the port since the announcement of the coup.
"Ambrey is aware that movements in and out of Gabon have been closed down following an early morning announcement by military officials," it added in an advisory.
(Reuters - Reporting by Jonathan Saul; Editing by Alex Richardson)