China will open a high-speed rail line to the North Korean border on Tuesday, state news agency Xinhua said, the latest effort to boost economic ties despite tension between the countries. The line, under construction since 2010, will run 207 km (127 miles) from Shenyang to the border city of Dandong, which faces North Korea across the Yalu River, and will shorten the train journey from 3 1/2 hours to just over one hour, Xinhua said. The new link will "raise the region's economic competitiveness", the report cited an unnamed railway official saying. As much as 80 percent of trade between China and North Korea passes through Dandong, which is near one of North Korea's special economic zones on Hwanggumpyong island. China has encouraged the development of three special economic zones in North Korea, hoping to tap low labour costs and encourage the North to see the benefits of economic reform, even while publicly rebuking it over its nuclear weapons programme. While there has been little sign of progress in the new economic zones, China continues to improve infrastructure on its side of the border, including building a bridge from Dandong into North Korea. As relations between China and North Korea have become strained in recent years, China has grown closer to South Korea, Asia's fourth-largest economy and the North's main rival.