The group of men stormed Kunming Station attacking passengers and staff.
Several of the killers were reported to have been shot by police.
Horrific pictures of dead bodies and scattered luggage in pools of blood started have been shared online.
The mass stabbing, which left at least 113 people injured, is one of the most grisly in China in recent years.
The state-run Yunnan News said the men were wearing uniforms and gunshots were heard after police arrived at the scene.
Local TV station K6 reported that several knifemen had been shot and victims had been taken to local hospitals after the “violent terror attack”.
The shocking scenes left passers-by in tears as police cleared the area amid fears knifemen were still in the area.
There was no information about who was responsible or their motives for the massacre, in Yunnan province, south-west China.
State TV said on its official microblog that China’s domestic security chief, Meng Jianzhu, was on his way to the station.
Mass stabbings are quite common in China but none have been reported recently on this scale and with this many fatalities.