Authorities in China's mainly Muslim Xinjiang mounted a mass sentencing in a stadium for 55 people on offences including terrorism, state media said Wednesday, as they press a crackdown on escalating violence.

About 7,000 people and Communist Party officials in Ili prefecture attended the "mass gathering for public sentencing, public arrests and public criminal detention, punishing a group of violent terrorist criminals in accordance with the law", official news agency Xinhua said in an online report.

Judicial officials at the stadium issued punishments for crimes including murder, separatism and organising, leading or participating in a terrorist group, as well as harbouring criminals and rape.

Three were sentenced to death for using hatchets and other weapons to murder a family of four last year "using extremely cruel methods", the report said.

At the stadium, police also announced the formal arrests of 38 suspects and detained another 27.

Photos showed armed officers guarding the premises, and the accused crammed into backs of lorries wearing orange vests and bent forward to face the ground as helmeted security forces stood over them.

The event was intended to demonstrate authorities' "resolute determination crack down on the 'three forces' of violent terrorism", Ili's deputy party chief was cited as saying, referring to separatism, extremism and terrorism.

"The guilty will not escape," he was cited as saying. "The only way out is to stop doing evil, turn yourself in and confess your crimes."

China used mass trials in the 1980s and 90s to try to combat the rise in crime driven by the social upheavals that accompanied the country's dramatic Reform and Opening economic overhaul, but the practice later faded.

- Year-long crackdown -

Beijing at the weekend vowed a year-long crackdown on terrorism following a string of attacks blamed on militants from Xinjiang, home to the Muslim Uighur minority, with violence in recent months increasingly targeting civilians and spreading elsewhere in China.

Last week five suspects killed 39 people and wounded more than 90 in a car and bomb assault on a market in the regional capital Urumqi.

On April 30, the final day of a visit by Chinese President Xi Jinping to the region, attackers armed with knives and explosives killed one person and wounded 79 at an Urumqi railway station.

In March knifemen killed 29 people and wounded 143 at a railway station in the southwestern city of Kunming, an incident dubbed "China's 9/11" by state media.

Authorities have boosted security across the country, taking the rare step of deploying more armed police in major cities, and arrested 200 people across Xinjiang over the past month.

A senior official in Ili came under investigation recently for "having an equivocal attitude toward violent terrorist incidents" and "sharing views in public places that were not in line with local policies", Xinhua reported on Tuesday.

Beijing says it faces a violent separatist movement in Xinjiang driven by religious extremism and backed by overseas terrorist networks.

But experts question how organised the groups in Xinjiang are, while rights groups point to cultural repression of Uighurs and economic favouritism towards an influx of Han Chinese, the country's ethnic majority, into the resource-rich region.

In 2009 riots broke out in Urumqi between Uighurs and Han that left 200 people dead.

Dilshat Rexit, a spokesman for the exiled World Uyghur Congress, said in a statement responding to the mass sentencing: "The judiciary has become a means of assisting China's crackdown against Uighurs.

"China's provocations will spur even more despairing Uighurs to fiercer resistance."