BEIJING — Attackers crashed a pair of vehicles and tossed explosives in an attack Thursday near an open air market in the capital of China’s volatile northwestern region of Xinjiang, leaving an unknown number of people dead and injured, state media reported.

The official Xinhua News Agency said several people were rushed to hospital and flames and heavy smoke were seen at the scene, which was cordoned off.

No other details were given and it wasn’t clear if anyone had been killed in the early morning blast in the city of Urumqi. A spokeswoman for the Xinjiang regional police department would only say that more information would be forthcoming.

“I heard four or five explosions. I was very scared. I saw three or four people lying on the ground,” said Fang Shaoying, the owner of a small supermarket located near the scene of the blast.

Photos from the scene posted to popular Chinese social media site Weibo showed at least three people lying in a street with a large fire in the distance giving off huge plumes of smoke. Others were sitting in the roadway in shock, with vegetables, boxes and stools strewn around them. Police in helmets and body armor were seen manning road blocks as police cars, ambulances and fire trucks arrived on the scene.

Urumqi was the scene of a railway station bomb attack late last month that killed three people, including two attackers, and injured 79. Security in the city has been significantly tightened since the attack, which took place as Chinese leader Xi Jinping was concluding a visit to the region.

The station attack and other violence have been blamed on radicals from among the region’s native Turkic Uighur Muslim population seeking to overthrow Chinese rule in the region.

Tensions between Chinese and ethnic Uighurs in Xinjiang have been simmering for years, particularly since riots in 2009 in Urumqi left nearly 200 people dead, according to official figures.

Information about events in the area about 2,500 kilometers (1,550 miles) west of Beijing is tightly controlled.

Copyright 2014 The Associated Press.