Separately, the municipal Ecology and Environment Bureau of Handan, another steel production hub in northern China, announced it will introduce the same level of emergency response from Friday.

Local steel mills will typically be required to curb production amid the emergency actions.

It is unclear when the pollution controls in both cities will be lifted.

(Reporting by Amy Lv and Dominique Patton in Beijing; Editing by Muralikumar Anantharaman)