Hong Kong's air pollution has reached a record high of 174 recorded in 2000, nine years ago.

According to the Hong Kong's Environmental Protection Department, the external conditions with air pollution index higher than 101 are not good for persons with heart or respiratory diseases.

So they are advised to stay at home and avoid going out.

The department said that a pall of smog is hanging over the city caused by the pollutants due to lack of the wind.

Taking the air pollution seriously, the Australian government has issued a health alert to its passengers earlier this year.

For the past 18 months, a thick fog has been developed over the city due to the mixing of emissions from the factory belt in southern China and local emissions from power plants and transport.