An explosion ripped through a fast-food restaurant in China Monday, killing at least seven people, injuring dozens 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 explosion, the official Xinhua news agency said.

Photographs taken outside the high-rise building in the northern city of Xian where the blast 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 it appeared to be a gas explosion at a restaurant serving traditional style hamburgers on the first floor of the building.

"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 was not clear.