A full deployment of security officials was underway at all eight terminals of Charles de Gaulle airport and its two railway stations, with reinforced checks on trains arriving from Brussels, an airport source said.
Additional patrols were also dispatched at Orly airport in southern Paris and the southern city of Toulouse.
Security was beefed up at train stations and on public transport in the capital, a police source added. French President Francois Hollande held a meeting with his prime minister and interior minister to discuss the attacks in Belgium, which have left at least 13 dead and 35 injured.
Security measures were also beefed up at London's Gatwick airport, at Frankfurt airport and airports in the Netherlands.