China has put troops stationed along its border with North Korea on high alert in case a war breaks out on the Korean Peninsula, Japan's Yomiuri Shimbun daily reported Tuesday.

The daily said this is the second highest of the People's Liberation Army's three alert stages, which goes into effect when a direct military threat has reached a certain level. It means weapons and troops are prepared for battle and all leave is canceled.

Sources told the paper the alert went into force around the middle of this month, and an extra 100,000 troops have been moved to the border.

Chinese President Xi Jinping toured border bases last Friday.

It was not clear whether the extra troops are there to handle a potential influx of refugees in the event of a crisis or whether they would march in.

China's state-run Global Times said in a recent editorial that Chinese military intervention would be "unnecessary" if the U.S. chooses to launch a surgical strike against North Korea's nuclear facilities, but added the red line would be U.S. or South Korean troops on the ground.

