Mongolia is working to clear a massive backlog of coal trucks queued for more than 100km at the Chinese border. The traffic jam has been caused by delays at the border check point which have been exacerbated by increasing coal sales to China.

Reuters reports that since China banned coal imports from North Korea, Mongolia has become one of China’s biggest coal suppliers. Restrictions on deliveries to some smaller Chinese ports have also contributed to increased demand from Mongolia.

Mongolia’s official Montsame news agency said this week that customs clearance at the Gants Mod border crossing on the main route to China were said to be taking as long as a month, up from the normal period of two weeks.

Ministry of Foreign Affairs state secretary D Davaasuren told a press briefing on Wednesday, “There was a problem at the border, so at the end of July and beginning in August, there were 400 to 500 trucks passing through the border gate.”

He said Mongolia had discussed the matter with Chinese officials and around 990 trucks entered China on Tuesday, which was closer to normal levels.

Montsame reported that last week Mongolia had mobilised to improve carrying capacity at border checkpoints and also promised to negotiate with Chinese officials to ease the bottleneck.

Chinese industry consultants sxcoal has reported that coal trucks were forced to wait two or three days before they were even permitted to unload for inspections at the border.

According to Reuters, China’s General Administration of Customs said on Wednesday that 2.26 million tonnes of non-lignite Mongolian coal were imported in July, up 32.4% from a year ago.

Mongolia has been China’s third-biggest source of coal imports over the first seven months of this year, with total shipments reaching 20.85 million tonnes, up 73% compared to last year.

With a long-awaited railway connection still unfinished after investment dried up, all coal from mines in Mongolia’s South Gobi region along the border with China are delivered via one single highway, making it vulnerable to disruptions.