An investigation is underway into what caused an apartment building under construction in the Minhang District of Shanghai to collapse.

Investigators are checking details relating to the 13-story structure, including its management, blueprints, and supervision of the construction. They've ruled out any possibility of a secondary accident.

The more than 130 families evacuated shortly after the collapse returned to their homes nearby on Sunday evening, after their homes were confirmed safe.

Meanwhile, sources say the local government has taken appropriate control measures against nine people from the real estate developer, its construction contractor and supervisor. The building fell down entirely at about 6 A-M on Saturday. One worker was killed at the site.