Ever more high-polluting industries in China

China's energy-hungry, high-polluting industries continued to grow too fast in 2013, putting "huge pressures" on the environment and causing air quality to worsen, according to the country's pollution agency.

Premier Li Keqiang "declared war" on pollution in a major policy address, but China has long struggled to strike a balance between protecting the environment and keeping up economic growth.

Read: Polluters will pay

China is still too slow in reforming its resource-intensive economy, the Ministry of Environmental Protection said in a statement on its website.

"The pace of restructuring and upgrading industries has slowed, the mode of development remains crude, and emissions of atmospheric pollutants have long exceeded environmental capacity," it said.

Heavy smoke alerts

Rapid urbanisation brought dust from new housing and road building, while more traffic increased emissions. Slower wind speeds than usual in northern China were an additional contributing factor last year.

Only three out of 74 Chinese cities fully complied with state pollution standards in 2013, the ministry said earlier this month.

Separately, the official Xinhua news agency said that the meteorological office had issued another heavy smog alert for Beijing, its neighbouring city of Tianjin and for the province of Hebei.

All-out effort to tackle pollution

The smog is expected to last until Friday, when it will be dispersed by a cold front, the report said.

Beijing's mayor promised in January to spend 15 billion yuan ($2.4 billion) on improving air quality this year as part of an "all-out effort" to tackle pollution, though similar pledges in the past have brought little improvement.

Pollution is an increasing concern for China's leaders, keen to forestall potential unrest as affluent city dwellers turn against the growth-at-all-costs economic model that has tainted much of the country's air, water and soil.

Thick blanket of pollution: Buildings are shrouded in smog on February, 20, 2014 in Beijing, China.