Officials in Mexico City have declared an environmental emergency after air pollution in the Mexican capital reached levels potentially dangerous to human health.

They urged those at particular risk to stay indoors and restricted the number of cars which can be driven in the city on Wednesday.

Smoke from nearby forest fires has contributed to the spike in pollution.

The city has been wrapped in a smoky haze for days.

Mexican photographer Santiago Arau tweeted video taken from a drone showing the extent of the pollution.