URUMQI, May 22 (Xinhua) -- An attack on a market in Urumqi that left at least 31 dead and 94 injured on Thursday morning was an act of terror, according to authorities.

It is the worst event in five years in the far western region after riots on July 5, 2009 in the regional capital claimed 197 lives and injured more than 1,700.

Two vehicles, without license plates, broke through roadside fences and plowed into people at an open-air market in Gongyuanbei Street near Renmin Park at 7:50 a.m. and explosive devices were detonated, said a statement by the Xinjiang Uygur Autonomous Region's publicity department.

Witnesses said explosives were thrown before the vehicles blew up.

A breakfast vendor told Xinhua he saw the two SUVs heading into the street at high speed and hitting people at random. "Four senior citizens were run over and killed in front of me," the vendor said.

A vegetable seller said the cars were weaving randomly. "The cars went past my stall, an old man near us was hit and I feared for my life," said the seller.

Many of the injured were elderly people who frequent the morning market.

At a local hospital, Turnisa Xadawut, 63, told how she lost three toes of her right foot in the explosion. Her five-months pregnant daughter, who accompanied her to the market, was burned on her face and feet, but luckily the baby appears to have been unharmed.

The Xinjiang Regional People's Hospital received 15 patients from the scene, two of whom were seriously injured. The youngest is 51 years old and the rest are all above 65, said Lei Wei, deputy head of the hospital's medical administration department.

"The injured include people from both Han and Uygur ethnic groups," said Liu Hongxia, head of the medical administration department of the regional traditional Chinese medicine hospital.

"Most of them are elderly people," said she in tears. "I feel sad seeing them suffer."

The cars came to a halt at the end of the street and the bombs were set off. An aquatic products shop near the first blast had all its windows broken.

The boss of the shop said the first car stopped because pedestrians had felled and vendors' carts blocked its way. "Two minutes later, the car exploded," the boss said.

A supermarket manager said that a lot of people had rushed to her store to hide. "People were screaming and crying. There was blood on some of them. It was horrible," she said.

A business owner in the market told Xinhua he heard a dozen big bangs.