When a red alarm is issued after 6am and before the start of classes, schools and kindergartens will not close but there will be no outdoor activities. However, students who don't attend class or arrive late will not be counted as absent.

Teachers and school staff are still required to be at work.

"Schools and kindergartens will still operate in case of a red alarm. Some students might miss the alarm and still attend class, and should still be taken care of by the school," said Wang Ping, vice director of the Shanghai Education Committee.

"There are also occasions when parents are too busy to take care of the children, and schools should still take the responsibility."

Schools and kindergartens will also be closed when weather alerts are issued in the event of extreme conditions such as typhoons, rainstorms, snowstorms and frozen roads. Boarding schools will cease outdoor activities.

The lowest air quality alarm, blue, will be issued when the city's AQI is forecast to be between 201 and 300 over the following 24 hours. If such a reading is expected to last for 48 hours, the alarm will turn to yellow.

An orange alarm will be issued when the AQI is predicted to be between 301 and 450 over the next 24 hours.

Potential sources of pollution — some enterprises and construction sites, for example — will receive reminders when a blue alarm is issued. Relevant government departments and organizations will be required to strengthen management over pollution sources.

Under a yellow alarm, the city will partially close construction sites. Factories discharging pollutants will be suspended and vehicles with construction materials banned from the roads.

Under an orange alarm, enterprises in the oil, chemical, steel and cement areas will be required to suspend operations.

Schools and kindergarten should stop outdoor activities and there should be no construction work outdoors.