The Beijing environmental protection bureau began a one-month intensive crack-down Thursday on some of the city's vehicles to counter worsening pollution.

The bureau said it would mainly focus on heavy freight vehicles, construction tippers, "yellow label" vehicles - those that fail to meet the European No 1 standard for exhaust emissions - and trucks registered outside the capital. Most vehicles are not allowed inside the Fifth Ring Road and are linked to issues of overloading and excessive emissions.

"These vehicles' main threat to the city is their heavy emissions," said Li Kunsheng, director of the vehicle emission management division of the city's environmental protection bureau.

"We will set more than 100 remote sensing monitoring points to check the emissions of passing vehicles," Li said.

Vehicles registered outside of Beijing that are breaking emission rules will be asked to leave immediately, Li said.

"This is actually all routine work, but we have increased our frequency of checks, have greater resources and are prepared to take tougher action," he said.

One explanation for the accelerated action might be that the city was ranked 28 out of 31 provincial capitals and municipalities nationwide last year, in the Beijing Environmental Statement 2009.

Wang Dawei, director of the atmospheric division of the Beijing municipal environmental protection bureau, said waste from daily life - especially emissions from vehicles - is a major concern of the bureau.

He estimated the total number of cars in Beijing will hit five million by the end of 2010, which would cause massive challenges to his division.

Wang noted this year's blue-sky target is 73 percent, down from 78 percent last year.

"We are trying to create solutions, such as removing heavily polluting vehicles from the streets and possibly to expand the no-car-day ban," Wang said.

In a recently-released announcement from the city's environmental protection bureau, a policy to eliminate "yellow label" cars in Beijing, by offering subsidies to their owners, was extended by seven months to Dec 31.

The policy successfully removed 106,000 "yellow label" cars from the city's streets last year, the first year it was implemented. Li said the policy was extended to guarantee the target of eliminating 40,000 cars this year. By the end of May, the figure was 13,000.

As to the no-car-day ban, the policy blocks certain license plate numbers from entering urban areas every five days. Wang's division is considering banning two license plate numbers every five days.