The Eiffel Tower is seen from a hot air balloon as Paris suffers a pollution spike, Monday Dec. 5, 2016. Paris authorities have adopted measures to limit traffic speed after high levels of pollution in the French capital. (AP Photo/Christophe Ena)

Paris has temporarily barred half of all cars from traveling on city streets and made public transportation free for the day as it battles a peak in pollution.

Facing red-alert levels of pollution since Nov. 30, Paris City Hall said the situation poses a significant risk to residents' health. Authorities say pollution is due to weather conditions and a heavy dependence on diesel fuel.

To tackle what City Hall describes as an "exceptionally serious" crisis, Paris's Velib bike-share and Autolib electric cars were made free Tuesday, as well as the Paris metro and bus services. In addition, only cars with even-numbered plates were allowed to drive Tuesday in the French capital and its close suburbs.

City officials say it's the ninth time this year that Paris is facing a pollution peak.

The Montparnasse Tower is seen from a hot air balloon as Paris suffers a pollution spike, Monday Dec. 5, 2016. Paris authorities have adopted measures to limit traffic speed after high levels of pollution in the French capital. (AP Photo/Christophe Ena)

The Invalides dome is seen from a hot air balloon as Paris suffers a pollution spike, Monday Dec. 5, 2016. Paris authorities have adopted measures to limit traffic speed after high levels of pollution in the French capital. (AP Photo/Christophe Ena)

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