Smog in and around Beijing has caused a 40-car pile-up in Tianjin and airport delays.

The unprecedented level of thick smog is causing havoc across northern China.

The pile up injured six people and caused a severe traffic disruption for morning commuters.

Adding to the mess, nearly 50 flights were delayed at Tianjin Airport.

Tianjin's air quality monitoring stations reported that air pollution had reached "hazardous" levels through the early afternoon.

Air quality in the Chinese capital has mostly stayed between "very unhealthy" and "hazardous" for about two weeks on an index that measures particulate matter in the air.

To help combat the smog, Beijing has temporarily shut about 100 heavily polluting factories and took 30 percent of government vehicles off roads.