Shanghai is suffering from its worst November air quality in five years after the local government lifted pollution controls that were in place for the six-month World Expo, state media said Thursday.

The air pollution index in the eastern metropolis has exceeded 100 - the level that Chinese environmental standards call "slightly polluted" - on eight separate days this month, the China Daily reported.

It called those readings the worst in five years.

On November 13, the index shot to 370, the highest level in the past decade, it said. A reading of 300 indicates "heavily polluted" air.

The city's air-monitoring agency has blamed the poor air quality on sandstorms from northern China, the report said.

However, the run of bad air coincides with the lifting of a moratorium on major construction during the World Expo, which ended on October 31.

A ban imposed by the local government on burning straw, which is a major source of air pollutants, also expired with the end of the Expo.

Thursday's air quality was "good", the air-monitoring agency said.