State media say the blast happened at the start of this morning's rush hour in a fast food restaurant in Xi'an (shee'-ahn).
The official Xinhua (shihn-wah) news agency says the blast likely was caused by a natural gas leak. The explosion knocked windows out as far as a mile away.
Photos on the website of the Xi'an Daily show the front of a building had been blown into a street where there were several bodies covered in blue plastic.
Reports say many of the victims, including children, were walking by the front of the restaurant or waiting for a bus.