China has executed eight people for alleged "terrorist" attacks across the country, including three who "masterminded" a car crash in the capital Beijing's Tiananmen Square last year, state media has said.

The official Xinhua news agency said on Sunday that the eight were involved in several cases in Beijing and in the restive far northwestern region of Xinjiang.

Three of the executed group "masterminded" the October 2013 attack in the heart of the Chinese capital, the report said. They were indentified by Xinhua as Huseyin Guxur, Yusup Wherniyas and Yusup Ehmet.

Five people were killed and 40 injured in the Beijing attack, when a car plowed into a crowd in the square and burst into flames.

State television showed images of the individuals who have been executed being led into court and questioned by the police. It also showed footage of the Tiananmen attack, with a car being driven into the square.

The five other executions, carried out in recent days, were punishment for crimes ranging from setting up a "terrorist" outfit and illegally making explosives to attacking police officers and killing government officials, Xinhua said.

Xinhua, which cited the Xinjiang region publicity department in its report, did not say when the executions were carried out.

Some of those executed were blamed for attacks in Xinjiang's prefecture of Aksu, the city of Kashgar and the town of Hotan, the agency added.

'Deprived of due process'

China has been cracking down on violent crime in Xinjiang after a string of deadly attacks there, and it executed 13 people in June.

Human rights activists, however, said that the suspects were deprived of due process that meets international standards. They also said that the government's own repressive policies have provoked unrest, an accusation Beijing denies.

Xinjiang is the traditional home of Muslim Uighurs who speak a Turkic language, and China has attributed attacks there to armed groups, which the government says seek to establish an independent state called East Turkestan.

Hundreds of people have died in the violence in the region over the last two years, with dozens jailed in the last month, some at mass public sentencings reminiscent of China's revolutionary-era rallies.

Authorities have tightened security around public transport in a bid to preempt violent attacks, demanding bus passengers show identification to travel.

This month a court in Xinjiang sentenced 25 people to jail for terror-related offences.

A suicide bombing in May killed 39 people at a market in Xinjiang's capital of Urumqi, while in March, 29 people were stabbed to death at a train station in the southwestern city of Kunming.

Beijing does not say how many people it executes each year, but independent estimates put the total at about 3,000 in 2012, a figure higher than all other countries combined.