Environmental inspectors in Beijing are scrambling to keep pace with a rising number of cases as the city tries to impose tough new standards on thousands of polluting firms, highlighting the growing logistical problems facing China's war on smog.

 The China Central Television (CCTV) building is seen next to a construction site in heavy haze in Beijing's central business district, in this January 14, 2013 file photo.

The Chinese capital has been at the frontline of a "war against pollution" declared by Premier Li Keqiang in March, and 652 industrial facilities were punished for breaching environmental regulations there in the first four months of 2014.

Beijing's efforts are part of a promise made by the central government to reverse the damage done by decades of untrammeled growth and beef up powers to shut down and punish polluting firms.

But the city's 500-strong squad of environmental enforcers have struggled to cope with the sheer volume of complaints.

"We have a total of 500 inspectors throughout the city, and it is certainly far, far from enough to ensure proper oversight," said Li Xiang, an inspector with the municipal environmental protection bureau.

Li was speaking at the team's headquarters in the northwestern outskirts of the city, where a fleet of grubby white inspection vans was being prepared for a new operation.

"Actually there are just too many cases," he added, noting that the city environmental bureau is now handling around 5,000-6,000 complaints a month.

"One after another they come to our department and it becomes impossible -- we can only adopt a guiding role and do our best to set up standard working procedures for the most important cases."

Making matters worse, some firms are slow to cooperate, with bosses refusing to sign documents, blocking vehicles from entering the premises and on occasion resorting to verbal abuse.

The problem is not just in Beijing, where harmful particle concentrations known as PM2.5 are 156 percent higher than the recommended national standard and over four times the daily level recommended by the World Health Organisation.

Hundreds of smaller, less prosperous cities across the country face even bigger challenges.

According to the Energy Foundation, a non-government U.S. advisory group, China had a total of 2,935 officials involved in environmental protection by the end of 2011, compared with 17,106 in the United States.

It also estimated that China's environmental budget in 2012 amounted to just $0.40 per member of the population, compared with $25 in the United States.

REGULATORY GAP

Researchers have said that while China's environmental legislation has improved in recent years, authorities have struggled to keep pace with the growth of the economy.

That expansion has brought thousands of polluting factories into existence without the equivalent increase in the state's regulatory powers.

"We have had this race between economic growth and environmental protection, and even though we have the policies, and even if they are effectively implemented, we are still quite overwhelmed by the rapid economic growth," said Qi Ye, director of the Brookings-Tsinghua Center for Public Policy.

Beijing has seen its population grow 66 percent and the total number of vehicles by nearly 200 percent between 1998 and 2012, putting huge pressure on regulators when it comes to implementing policies like fuel standards.

Li Kunsheng, director of the vehicle emissions centre of the Beijing Environmental Protection Bureau, told Reuters that while Beijing only permits vehicles that conform to tough fuel standards, the city has neither the technology nor the boots on the ground to enforce its rules.

"We check local cars very strictly, but for those coming into the city from outside, we can only rely on transport police to stop and check them," he said.

"Large numbers of vehicles have problems, and relying on this method doesn't really solve anything."

Last month, China passed long-awaited new amendments to its 1989 Environmental Protection Law, giving legal backing to the army of environmental inspectors and promising additional powers to monitor and punish violators.

"The new environmental law does have something to say about expanding environmental enforcement powers, so we will certainly get bigger," said Yan Xiangyang, head of the Beijing environmental bureau's inspection office.

"We will certainly get stronger, but I can't say how many more people we will get. That isn't our decision."