Beijing’s pollution index hits its highest measurement level Friday and authorities warned people to stay indoors as a murky grey haze settled over the Chinese capital.

The Beijing Environmental Protection Bureau said pollution had hit the heaviest level on the one-to-five scale five during the 24-hour period from noon Thursday. “The city is experiening weather that is not beneficial to dispersing pollutants, so the city’s emissions continue to concentrate creating a thick haze of pollution,” it said on its website.

“Even under conditions of light winds, changes in temperature, high humidity and fog, the situation has only worsened.”