In Guangzhou, home to more than 10 million people, the number of smoggy days surged to 120.4 last year, the second highest on record since 1950, another official study said. The Guangzhou Observatory issued six severe smog warnings last year when pollutants reduced visibility in the city to less than 2km.

The smoggy atmosphere has seen a sharp increase in the number of patients suffering from various respiratory diseases. It also significantly reduced the hours of sunshine in the Pearl River Delta. The average number of sunny hours in Guangdong was 1,622 last year - 160 hours less than normal but 16 hours more than in 2005, the report said.

Surprisingly, the report by the provincial Statistics Bureau left out any mention of acid rain - which has become a serious environmental problem in the Pearl River Delta in recent years. But in its report last year, the frequency of acid rain in Guangdong was reported to have jumped from 40.5 per cent in 2002 to 55 per cent in 2005.

Another official study has said the frequency of acid rain in Guangzhou surged a staggering 74 per cent last year. The study attributed the problem to industrial and vehicle emissions.

The latest statistics are an embarrassment to Guangdong's leaders, who have repeatedly pledged to clean up the environment. In its environmental protection roadmap for the period between 2006 and 2020, the provincial government had promised to reduce industrial emission levels and improve air quality. It had said that by 2010, half of the towns in Guangdong would reach 'model city standards' - but did not elaborate.

Environmental experts said the government needed to rethink its development planning if it wanted to meet the targets.

'Guangdong invested a lot [in 2006] to develop heavy industry. The overall industrial pollution therefore increased,' said Kuang Yaoqiu , a researcher from the Chinese Academy of Sciences. 'Although we have improved our energy efficiency and used fewer resources to produce the same amount of products, as a whole we did generate more pollutants than before.'

He said the Guangdong government had focused its industrial development too narrowly on the Pearl River Delta and urged the government to move some of the industries out of the delta.

Professor Kuang also criticised the decision to turn Nansha port in Guangzhou into a petrochemical and heavy industry centre.

'The location of Nansha is very bad for heavy industry because it is at the heart of the Pearl River Delta. The pollutants it generates can easily spread to other cities or get trapped,' he said.

'Many [environmental experts] have voiced concerns about such planning. Unfortunately, the local government cares more about tax revenue and other factors. If it does not change its mindset, the pollution problem will stay.'