Paris authorities have requested emergency traffic-limiting measures to be put in place on Friday, as the City of Light and much of northern France suffers from a choking smog.

City Mayor Anne Hidalgo asked national authorities to stop one in every two cars entering the capital and make all public transport free for a day in a bid to drive down pollution.

These emergency measures were last implemented almost exactly a year ago - on March 17 - during a particularly bad spike in pollution levels.