A "strike hard" campaign against what China calls terrorism in the largely Muslim region of Xinjiang and beyond has seen 181 gangs busted, authorities said Monday, a year after the controversial measures were launched.

Rights groups have labelled the crackdown discriminatory, raising further concerns after Beijing announced in January the measures would be extended until at least the end of 2015.

China has executed three people for a mass stabbing that killed 31 people last year, the country's top court said Tuesday, with authorities blaming the attack on separatists from mainly Muslim Xinjiang.

Iskandar Ehet, Turgun Tohtunyaz and Hasayn Muhammad were put to death for "leading a terrorist organisation and intentional homicide", the Supreme People's Court said in a microblog post.

China convicted and sentenced 712 people for terrorism, separatism and related crimes last year, the country's top court said on Thursday, saying such offences were its top priority for 2015.

Violent attacks and unrest have been on the rise in recent years in China's remote Xinjiang region, home to the mostly Muslim Uighur minority, and Tibetan areas, where reports of self-immolation in protest against Chinese rule often hit global headlines.

A Chinese appeals court on Friday upheld death sentences for three people convicted over a mass stabbing that killed 31 people earlier this year, state media reported.

"The Higher People's Court of Yunnan Province rejected Hasayn Muhammad's appeal and upheld the penalty meted out by the Kunming Municipal Intermediate People's Court last month," Xinhua said in a brief dispatch from Kunming.

Knife-wielding assailants left 29 people people dead and more than 130 wounded in an unprecedented attack at a Chinese train station, state media reported Sunday, blaming separatists from Xinjiang.

Victims described attackers dressed in black bursting into Kunming station in the southwestern province of Yunnan and slashing indiscriminately as people queued to buy tickets, prompting shock and outrage.