Beijing was shrouded in heavy smog on Thursday with AQI climbing to “very unhealthy” levels of 215, a rare spike in pollution in the Chinese capital after years of expensive cleaning up.

China’s national observatory on Wednesday issued a yellow alert for heavy fog in some parts of the country, saying that thick fog is expected to shroud parts of Hebei, Beijing, Tianjin, Henan, Anhui, Jiangsu, Hubei, the Sichuan Basin and Chongqing on Thursday.