The killing spree occurred at about 9 p.m. in Yongling township in Xinbin Manchu autonomous county in the city of Fushun, the Fushun city’s publicity department said in a statement.
The 17-year-old suspect, a native of Xinfu district in downtown Fushun, stabbed to death two relatives of his girlfriend after having conflicts with his girlfriend, an initial investigation showed.
The teenager, surnamed Li, killed another six people and injured five while fleeing the scene, it said.
The killer has been held by police.
A further investigation into the killing is under way.
Violent crimes are growing more common in China. There was a string of knife attacks against schoolchildren across the country in early 2010 that killed nearly 20 and wounded more than 50.