Beijing, Mar 1 (IANS/EFE): Pollution in Beijing and surrounding areas Thursday returned to dangerous levels for the second time in a week, Chinese environmental authorities said.

The air pollution has been aggravated by a sandstorm originating in Inner Mongolia.

The concentration of tiny particulate matter in the air, considered especially dangerous due to its ability to get into the lungs and the bloodstream, exceeded 400 micrograms per cubic meter, according to measurements made by the Environmental Control Center in Beijing.

According to the equipment installed at the US Embassy in the Chinese capital, the concentration Thursday morning exceeded 500 micrograms and the poor air quality index reached 516 points, which is above the 500-point level considered to be the maximum (or worst) on the scale.

Poor visibility in the capital area has led to the cancellation of flights at the Beijing airport.

The heavy air pollution registered in China's main cities in January and February has increased concerns about the country's environmental situation as well as pressure on Beijing to accelerate measures to reduce pollution, including imposing a tax on carbon dioxide emissions.