"These two years will be the worst," Sarah Liao, Minister for the Environment, Transport and Works, told legislators.

Officials on both sides have blamed poor air quality on power plants and the ever-increasing population of cars and factories.

Liao said Hong Kong and Guangdong would implement a series of measures to curb pollution in the coming years but it will take time before any improvement is visible.

Some of these measures include requiring power plants to build facilities to minimise emissions of pollutants and that will take time to install.

"If you want to see any improvement in regional air quality, you will have to wait till 2007," Liao said.

In a document, the government said authorities in Guangdong's Pearl River Delta, where factories are concentrated, will begin monitoring air quality in 2005.

Hong Kong and Guangdong previously agreed to dramatically reduce by 2010 regional emissions of sulphur dioxide, nitrogen oxides and other pollutants.

To achieve this, they would impose ceilings on the total emissions of power companies and require them to maximise the use of natural gas and develop renewable energy for power generation, according to the document.

Hong Kong will also soon begin to impose charges for construction and demolition waste.