According to local government officials, nine people were working on an underground project when the accident took place on a section of the subway line No 3 located at the provincial capital Xi'an.
They added that four people were pulled out immedietly after the accident, including three who were unhurt and one who has suffered from fracture.
The injured has been sent to a local hospital and rescue work is still underway while safety measures have been put in place to prevent secondary disasters, state run Xinhua News Agency reported.