BEIJING, July 30 (Xinhua) -- China's environment authorities are to ban motor vehicles registered outside Beijing from entering the capital city if they fail to meet exhaust emissions standards.

    The Ministry of Environmental Protection said Thursday that from Oct. 1, petrol vehicles would not be allowed to travel along or within Beijing's Sixth Ring Road, the city's outermost highway loop, if their exhaust emissions do not comply with National Emission Standard I.

    Diesel-driven vehicles must comply with National Emission Standard III or above before they can operate in the same area.

    Cui Mingming, an official with the ministry's department of pollution control, said the new rule applied to vehicles registered outside Beijing because many regions have not yet made the standards mandatory.

    In order to further reduce pollution caused by car exhausts, vehicles entering Beijing must comply with the standards that 3.7 million local vehicles already do, she said.

    The rule would likely affect old vehicles because harsh emission standards are already applied to new cars.

    Standard I, which is equivalent to the Euro I standard, allows an average petrol sedan to emit a maximum of 2.7 grams of carbon monoxide a kilometer among other exhausts, whereas Standard IV requires less than 1 gram of carbon monoxide and 0.08 gram of nitrogen oxide per kilometer.

    China introduced Standards I, II and III respectively in 2000, 2005, and 2007. Standard IV will be adopted nationwide in 2010.

    Beijing became the first Chinese city to enforce Standard IV on newly bought and produced cars on March 1, 2008.

    Other cities such as Shanghai and Guangzhou are also moving to lower car exhaust emissions in attempts to address growing pollution concerns.

    It was still necessary to continue efforts in different parts of China to limit exhaust emissions from both new and used vehicles, Cui said.

    The ministry issued a notice early this week, requiring vehicle owners outside Beijing to obtain a clearance certificate from local environment authorities if they did not want to be blocked from entering Beijing.

    Traffic police are to carry out checks on major highways leading to downtown Beijing from Sept. 1.

    The ministry also warned car owners and local authorities not to fake the certificate.

    This is the latest step in Beijing to address growing concerns about air pollution as the number of cars there has rapidly reached 3.7 million.

    During the Olympics and Paralympics last year, Beijing limited the use of most vehicles through an odd-even license plate system. The initiative took 45 percent of the cars off the roads and helped keep skies clean.

    In April, the city implemented a new restriction, also based on license plates, which forces a fifth of privately-owned vehicles off the roads each week day.