An explosion ripped through a fast-food restaurant in China Monday, killing at least nine people including a child and shattering windows up to three kilometres away, officials and state media said.

Among the victims were children who were passing by the building on their way to school at the time of the blast, the official Xinhua news agency said, adding that another 34 were injured, seven of whom were in critical condition.

Photographs taken outside the high-rise building in the northern city of Xian where the explosion occurred showed shattered glass and piles of debris on the road outside the building, where bodies covered with blue sheets lay on stretchers.

Xinhua quoted local officials and witnesses as saying the blast appeared to be a gas explosion at a restaurant on the first floor of the building which served hamburgers cooked in a traditional local style.

"Thirteen people were sent to our hospital, and three died -- two male adults and a three-year-old girl. One is in a critical condition," a doctor surnamed Han at the Shaanxi Renmin Hospital told AFP.

Another 19 people injured in the blast were sent to the Xian Gaoxin Hospital and four of those had died, a nurse surnamed Wu told AFP. The condition of the other 15 people there was not clear.

The body of one victim, a woman, was found in the ruins of the restaurant, in an office tower in the Gaoxin district of Xian, Xinhua said.

Photos posted online showed a number of ambulances and fire engines on the street outside the building, called Jiatian International Mansion.

Other photos showed plumes of smoke coming out of the building and firemen walking over piles of debris that had been blasted onto the footpath.

The explosion appeared to have shattered the windows of the first two floors of the tower, with glass, mangled parts of the building and other debris littering the ground.

The force of the blast destroyed a bus stop, broke window panes two to three kilometres (1.2 miles to 1.9 miles) from the site, and obliterated dozens of cars parked nearby, Xinhua said.

"The blast knocked me down with glass fragments hitting my body from head to toe," Gong Yejian, an 11-year-old student passing by the building when the explosion hit, was quoted as saying.

"The tree near me fell down as well."

An official at the local public security bureau told AFP that emergency workers were still attending to casualties and they did not yet know the total number of dead and injured.

According to an initial probe, a gas leak was to blame for the blast, and authorities have suspended gas supplies for residential buildings near the accident zone, fearing more explosions, Xinhua said.

China has a notoriously poor record of workplace accidents, blamed on widespread disregard for basic safety measures as companies chase profits.

A coal mining accident in the southwestern province of Yunnan last week killed at least 34 workers, with hopes fading of finding alive nine others still trapped underground, officials said Monday.

Earlier this month, two vehicles carrying explosives detonated in the southwest province of Guizhou killing at least seven people, seriously injuring 20 and causing several nearby buildings to collapse.

The two vehicles were transporting 70 tonnes of explosives, state media reported.