BEIJING (REUTERS) - China's capital Beijing will set up cameras at building sites across the city to monitor how much construction contributes to Beijing's notoriously polluted air, state media said.

Air quality in cities is of increasing concern to China's stability-obsessed leaders, anxious to douse potential unrest as a more affluent urban population turns against a growth-at-all-costs economic model that has poisoned much of the country's air, water and soil.

Despite the billions of dollars spent on cleaning up the air, smog remains a major problem, especially in Beijing.

By the end of June, all building sites in the city will have to install cameras to assess how constructors' practices add to the capital's smog, Xinhua news agency said on Sunday.

"Based on the pictures taken by the cameras, the municipal commission of housing and urban-rural development will punish companies that use unqualified trucks to carry earth or allow outdoor construction to continue in heavily polluted days," the report said.

In addition, all building firms will have to use fully enclosed vehicles to carry earth from July 1, to prevent it from being blown into the air and adding to pollution, Xinhua added.

Construction sites are already closed on badly polluted days in Beijing.

The government will also demand contractors place funds for dust control in special bank accounts before construction, it said.