More than 1,500 factories in southern China had been closed down in the past three years due to the pollution and environmental hazards they posed.

The clampdown was part of Guangdong province's measures to combat worsening pollution in the booming Pearl River Delta manufacturing region and neighbouring Hong Kong, said Guangdong Environmental Protection Bureau director Li Qing.

A power plant on the outskirts of Zhangjiakou. More than 1,500 factories in southern China had been closed down in the past three years due to the pollution and environmental hazards they posed.[AFP/file]

More than 1,500 factories had been shut down after checks were made on 110,000 companies, he said.

Most of the affected businesses were cement and power plants, some of which were Hong Kong-owned, he was cited by Hong Kong's RTHK radio as saying.

Li said more measures were in place to reduce emissions of sulfur dioxide from power plants in the next few years.

His comments came before Hong Kong chief executive Donald Tsang was due to attend the Hong Kong-Guangdong Co-operation Joint Conference in Guangdong on Wednesday.

Ways to tackle rising pollution are expected to be high on the agenda of their discussions.

The talks are the latest effort from Tsang, who recently urged Hong Kong citizens to reduce electricity usage in order to cut emissions from power stations, in his battle to clean up the city's air.

Air quality has deteriorated in Hong Kong so much that smog reduced visibility to less than a kilometer (about half a mile) on more than 50 days last year, a record in this southern Chinese territory.

Companies say they are finding it hard to attract executives from overseas because of the pollution problem, and the travel industry says tourists are increasingly suffering smog-related health problems.

The government says the problem is mostly the result of the industrialisation of the neighbouring Pearl River Delta region, while green groups blame it on Hong Kong's coal-burning power stations and creaking diesel-powered buses.

In 2002, the Hong Kong and Guangdong governments agreed to reduce the emission of four major air pollutants including sulphur dioxide by up to 55 percent by 2010.

But green groups have criticised the standard as being too low.