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.