According to eyewitnesses, quoted in Chinese state media, two 4x4 vehicles drove into a crowd of people in the centre of the city, which is the regional capital of the far western Xinjiang Province.

Pictures posted on China's version of Twitter, Weibo, show victims lying in a street strewn with debris.

One picture shows officials carrying a man with a badly blooded head.

The pictures were taken by eyewitnesses moments after the explosion and show flames rising from the market which, shortly before 8am, would have been busy.

On Weibo, one user with the alias "Clarence-DD" described what he saw: "(It) was only 300 metres from my home, so close. I don’t know if it will happen to me next time. I only hope all are safe."

Another eyewitness, alias "Paikeluotuoci" posted: "It was before 8 this morning, (there were) several explosions took place near the Wenhuagong morning market, I was there, less than 100 metres away, I can see big smoke and people running around."

A user with the alias Suisuibusui wrote: "Two vehicles broke through police barrier, and drove into the morning market together, detonated explosives. 5 or 6 big sounds could be heard. One can smell the explosives from the north gate of the park."

The head of the Ministry of Public Security, Guo Shengqun, is on his way to Urumqi from Shanghai where he had been attending a major summit of Asian nations.

Meng Jianzhu, an official from China's Politburo, the top government body, has pledged that all will be done to help those caught up in the attack and rescue all those injured.

Xinjiang Province is the traditional home to China's Uighur Muslim population.

Over the past decade or so, an influx of the country's majority Han Chinese population has caused the Uighur community to complain of an erosion of their culture, their religion and their freedoms.

With a growing and worrying frequency, this resentment has manifested itself with violent attacks against government institutions and the Han Chinese population.