Unsafe tunneling in a high-risk area and a failure to reinforce the tunnel promptly after the initial collapse were blamed for a deadly accident in south China's Guangdong province, according to an investigation report released on Monday.

A ground collapse at a Shenzhen-Jiangmen Railway construction site in Shenzhen left 13 workers dead on Dec. 4, 2024.

The investigation found that as the tunnel advanced into a high-risk section, the surrounding rock had proved weaker than indicated in the original survey and design, but excavation had not been halted and no safer excavation or support methods had been adopted, leading to a partial collapse above the tunnel face, per the report, which was approved by an investigation team dispatched by the provincial government.

After the danger had emerged, a failure to take timely and effective engineering measures resulted in repeated collapses above the tunnel, causing the ground to cave in and killing workers on the surface.

The collapse also exposed problems related to inadequate management, weak risk control during construction, incomplete emergency-response mechanisms and the improper handling of the emergency on site.

The incident resulted in direct economic losses of approximately 72.6 million yuan (about 10 million U.S. dollars), said the report, which recommended that emergency management authorities hold those responsible to account in accordance with the law.