But the South China Morning Post reported that the WHO standards could not be met, even if local emissions were eliminated, without drastic measures across the border in mainland China.

Environmentalists have criticised the government for using "outdated" air quality measures adopted back in 1987 by the WHO. They were revised in 2000 but have not been amended by the local government.

The new WHO guidelines, outlined in a document released by the government on Monday, are far more stringent than the existing ones and include a standard for very fine particles that the city does not have.

The newspaper said a committee of government officials, experts and academics would oversee a study to be launched early next year on how to comply with the WHO guidelines, due to be released in September.

The study will also assess economic implications, time frame, interfaces with the mainland and impact on various policy areas before driving "practical and achievable options", the newspaper said.

Public consultation will be launched in 2008 before a set of new air quality objectives and an action plan are finalised, it reported.

Although the government has said combating pollution is its top priority, environmentalists criticised the study period as being too long.

A recent health study conducted by three Hong Kong universities and local policy think-tank Civic Exchange estimated that pollution was the cause of 2,000 deaths a year in the city, where poor visibility dominates 45 percent of the year.

It blamed the worsening situation on pollutants emitted from power plants, cars and factories from Hong Kong as well as the booming manufacturing cities of the adjacent Pearl River Delta in southern China.

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