Paris offers free public transport to reduce severe smog
Authorities in Paris have taken the rare step of making public transport free for three days to reduce severe smog caused by unusually warm weather.
The French capital region and 30 other departments have been on maximum pollution alert for several days.
Landmark buildings like the Eiffel Tower were barely visible after a white fog settled over Paris.
The capital's air quality has been one of the worst on record, French environmental agencies say.
A lack of wind, combined with cold nights followed by unseasonably warm days, has contributed to the worsening conditions.
The smog has also affected neighbouring Belgium, where officials have reduced the maximum speed limit allowed on main roads. The southern Wallonia region said it had also decided to make buses, trains and underground trains free until the pollution emergency was over.