China is to raise the coke export tariff rate to 40 percent as of August 20, up from 25 percent, said the State Council's customs tariff commission on Friday.

This move aims to ease a tight coke supply in domestic markets and to contain export of products with high pollution and energy cost.

China is the world's biggest coke exporter, which accounts for 60 percent of the coke trade volume.

Despite some western country's move in reducing coke production for environmental reasons, China's coke exports have continued to increase in recent years.

Coke exports surged to 14.5 million tonnes in 2006, representing an increase of 14 times in 15 years since 1991. The figure hit a record 1.66 million tonnes in May this year.

The nation's coke exports, however, hit a turning point in July, when the government decided to adjust its export policy to tackle the problem. Coke export in July fell to 830,000 tonnes, down 10 percent year on year.

China's move in raising export tariffs indicated that the government had made its decision to reduce coke exports, said market analysts.