China must stop hindering the flow of North Koreans seeking to escape hunger and poverty in the world’s most isolated country, while other world powers should back up their tough resolutions with action, the International Crisis Group says in a report on the plight of North Korean refugees.

While international attention is on Pyongyang’s nuclear programme, the think-tank warns that a humanitarian challenge is looming as widespread food shortages are likely to propel more starving North Koreans into China, a country taking increasingly tough steps to stop border crossers.