China is to open a high-speed rail line to the North Korean border this week, reported Xinhua in the latest move to boost economic between the two countries.

The line, under construction since 2010, will run 207 kilometres (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, said Reuters.

As much as 80 per cent 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.