More Chinese cities are issuing their first red alerts for pollution in response to forecasts of heavy smog after the capital, Beijing, issued two this month after coming in for criticism for not releasing them earlier.

Shandong province in eastern China issued alerts in four cities after warning that the density of particulate matter in the air would exceed high levels for more than 24 hours. Shandong environmental protection bureau said the alerts started Thursday morning.

Meteorological authorities in Hebei, regarded as China's most polluted province, issued the province's first red alert for smog on Tuesday.

Cities in Hebei then took response measures. Xingtai and Handan instigated traffic control measures to take half the vehicles off the road on a given day, according to Hebei's environmental protection bureau.