BEIJING — A Chinese county along the border with North Korea is constructing refugee camps intended to house thousands of migrants fleeing a possible crisis on the Korean Peninsula, according to an internal document that appears to have been leaked from China’s main state-owned telecommunications company.

Three villages in Changbai County and two cities in the northeastern border province of Jilin, have been designated for the camps, according to the document from China Mobile. The document appeared last week on Weibo, a microblogging site.

The camps are an unusual, albeit tacit, admission by China that instability in North Korea is increasingly likely, and that refugees could swarm across the Tumen River, a narrow ribbon of water that divides the two countries.

For decades, Chinese policy on North Korea has centered on maintaining stability in a neighboring country known for its repression and volatility.