China has sentenced nine people to death on terrorism-related charges in its ethnically divided western region of Xinjiang, state media said Thursday, as authorities crack down following several deadly attacks.

Multiple courts in Xinjiang sentenced 81 suspects on various terror-related charges, state-broadcaster CCTV said.

In the past year Xinjiang -- home to the mostly Muslim Uighur minority -- has seen an increase in violent clashes, which Beijing blames on organised terrorist groups seeking independence for the region.

Critics say Beijing exaggerates the terror threat in Xinjiang to justify hard-line measures, and point to economic inequality and cultural and religious repression of Uighurs as causes of unrest.

Also on Thursday, 29 people described as "terrorist suspects" were detained in Xinjiang's capital Urumqi on charges including "inciting separatism" and "gathering mobs to disturb order in a public place", the state-run Xinjiang Net said.

The 29 cases were processed according to new rules calling on state prosecutors to complete terror-related investigations within 24 hours, the report said.

China last month vowed a year-long campaign against terrorism, after attackers in Urumqi killed 39 people in a suicide raid on a marketplace.

Assailants armed with knives and explosives carried out an attack at a railway station in the city in April, killing one person and wounding 79 as President Xi Jinping visited the region.

Authorities in Xinjiang last week sentenced 55 people for offences including terrorism at a mass sentencing in a stadium attended by about 7,000 people. Hundreds of others are reported to have been detained in recent weeks.

Rights groups have expressed concerns about whether terror suspects in the region are granted fair trials, given the common use of forced confessions in the Chinese legal system.

"Lack of justice and legal procedure will lead to more people losing their freedom for political reasons," Dilshat Rexit, a spokesman for the exiled World Uyghur Congress, said in a statement.

Information about Xinjiang, a vast and resource-rich region bordering Central Asia, is difficult to verify independently, with foreign and local journalists subject to heavy restrictions.