A state-run newspaper has argued in an editorial that China should remain neutral if North Korea attacks the U.S., but intervene forcefully if the U.S. strikes first. Excerpt via Reuters:
"It needs to make clear its stance to all sides and make them understand that when their actions jeopardize China's interests, China will respond with a firm hand. China should also make clear that if North Korea launches missiles that threaten U.S. soil first and the U.S. retaliates, China will stay neutral. If the U.S. and South Korea carry out strikes and try to overthrow the North Korean regime and change the political pattern of the Korean Peninsula, China will prevent them from doing so."
A word of caution: While the newspaper, the Global Times, is published by the official party organ, the People's Daily, it should not be interpreted as official government policy.