BEIJING (REUTERS) - China has sent teams of investigators to parts of the country worst hit by air pollution as part of efforts to stop the heavy smog engulfing about 15 percent of the country, including Beijing.

Twelve teams of inspectors will head to the cities of Beijing, the nearby city of Tianjin and Hebei province to see how authorities are responding to the worst air pollution in months, the Ministry of Environmental Protection said on Sunday.

The inspectors will visit construction sites and factories producing steel, glass, cement and coal products, the ministry said. Those found to be violating production standards will be publicly identified.

Authorities have issued innumerable orders and policies to try and clean up the environment, investing in projects to fight pollution and empowering courts to mete out stiff penalties. But enforcement has been patchy at the local level, where authorities often rely on taxes paid by polluting industries.

In Beijing, which has been shrouded in smoky, white smog for a week, authorirites raised the air pollution alert system to"orange" for the first time on Friday after drawing public fire for its initial ineffective response.

The "orange" level, the second-highest level of a four-tier system, advises schools to cancel sports classes.

Other emergency measures include cutting private use of cars by about a fifth in Shijiazhuang, a city near Beijing, state news agency Xinhua said. Authorities also banned barbecues and halted construction work.

It is not uncommon for air pollution in parts of China to breach levels considered by some experts to be hazardous. That has drawn much public ire and is a worry for China's government, which fears any discontent that might compromise stability.

"The Beijing smog has lasted for so many days. I feel like I have not seen the sun in a long time," said one user of Weibo, China's version of Twitter.

"O environment, are you going to let people live or not?"