By Mark Stone, China Correspondent, in Beijing
An explosion at a market in the Chinese city of Urumqi has killed 31 people and left more than 90 injured.
According to witnesses quoted in 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 northwestern Xinjiang Province.
Picture apparently showing the explosion in the market Pic: Weibo
Explosives were thrown from the vehicles, and one of the vehicles exploded, said Xinhua news agency.
The attack was described by China's Ministry of Public Security as "a serious violent terrorist incident of a particularly vile nature".
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 witnesses 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."
Urumqi is the capital of Xinjiang Province
Another witness, 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."
Victims lying in a street full of debris Pic: Weibo
In a statement, Chinese President Xi Jinping said his government will "swiftly solve the case, harshly punish the terrorists, promptly recover the dead and treat the injured, offer condolences to the families of the injured, and strictly prevent any ripple effects to materialise from this."
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, said all will be done to help those caught up in the attack.
The market was busy at the time of the blast. Pic: Weibo
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 in violent attacks against government institutions and the Han Chinese population.
Attackers killed 29 people in Kunming train station in March
Three weeks ago, on the final day of a visit to the region by President Xi Jinping, a knife-wielding group attacked passengers at a train station in Urumqi.
One person was killed and 79 injured. The two attackers were killed by Chinese security personnel.
In March, a group of attackers stabbed to death 29 people on the concourse of Kunming train station in central China. A total of 143 people were injured.
A vehicle crashed into a crowd in Tiananmen Square last October
The incident, described within China as the country's 9/11, signalled to the Chinese government that Uighur extremist groups were capable of operating well outside Xinjiang province.
In December, a vehicle drove into railings in front of the iconic Tiananmen gate at the northern end of the hugely symbolic square in Beijing.
The Chinese government said the three occupants were all Uighur Muslims. They all died along with two tourists.