China will take action against highly-polluting diesel trucks by imposing tougher fuel and engine standards, raising rail freight volumes and strengthening its monitoring capabilities, new guidelines published by the environment ministry said.

The Ministry of Ecology and Environment said in a policy document on Friday it would aim to "significantly increase" the number of diesel trucks capable of meeting emission standards by 2020, targeting a compliance rate of at least 90 percent by next year.

It also promised to improve the quality of diesel, crack down on low-grade fuel and reduce overall nitrogen oxide and particulate matter emissions from fuel combustion.

New trucks that fail to comply with state requirements will not be allowed to enter the market, and key regions will also be ordered to implement advanced "China VI" fuel standards starting in July this year, the document said.

China is in the fifth year of a "war on pollution" but average emission levels in many smog-prone northern cities remain significantly higher than the levels recommended by the government.

The northern regions near the capital Beijing will eliminate more than 1 million outdated diesel-fueled trucks by the end of 2020. Tougher controls on diesel freight will also be imposed during smog build-ups, it said.

National rail freight rates would be increased by 30 percent compared with 2017, and China will work to ensure that long-distance bulk commodity deliveries are done via rail or ships, it said.

Tackling truck emissions has become a major part of China's efforts to curb pollution. Though trucks produce 13 times more pollution per unit of cargo than trains, the share of rail in total freight amounted to just 7.7 percent in 2017.

The environment ministry said last year that while diesel trucks accounted for just 7.8 percent of China's total vehicles, they contributed as much as 57.3 percent of total nitrogen dioxide emissions and more than three quarters of airborne particulate matter.

The ministry plans to charge higher fees and introduce more stringent monitoring procedures to try to persuade firms to make better use of the rail network to deliver goods.