A total of 12 schools equipped with broadcasting facilities were giving lessons online on Tuesday, the first school day of 2017 and the third day of the city's top level smog alert, said an official with the city's educational bureau.

At 18 minutes per session, classes include major teaching content of the current curriculums at various grades, said the official.

All primary and high school students were encouraged to access the city teaching resource sharing website. Local educational cable television has also been arranged for elite courses during the smoggy weather, he said.

Xi'an city initiated the first level response for heavy air pollution at 6 p.m. on Sunday, requiring all schools and kindergartens to suspend classes.