Authorities in Qinghai Province, China, have launched a full-scale investigation into a deadly bridge construction accident that killed at least 12 workers and left four others missing. The incident occurred early Friday morning on the Qinghai section of the Xining-Chengdu Railway in Jainca County, Huangnan Tibetan Autonomous Prefecture.

According to the provincial emergency management bureau, the accident happened around 3:10 a.m. when a steel cable suddenly snapped during a tensioning operation. The failure caused a 108-meter-long steel girder arch rib to collapse. Sixteen workers were at the site when the collapse occurred, and several fell into the Yellow River.

Rescue operations were immediately launched. By Friday afternoon, more than 800 personnel, 91 vehicles, 27 boats, a helicopter, and five robots had been deployed to assist in recovery efforts. Six local hospitals were designated to provide emergency medical care.

China’s Ministry of Emergency Management dispatched a special working group to the scene to oversee rescue efforts and ensure that all missing workers were located. Provincial officials have formed a four-part investigation team tasked with coordination, technical analysis, management review, and rescue evaluation.

The Office of the Work Safety Commission under China’s State Council has also set up a dedicated working group with related ministries to lead the probe into the causes of the disaster. A report outlining the causes, responsibilities, and potential disciplinary or legal actions is expected soon.

The bridge, a steel truss arch design spanning the Yellow River, was a key part of the Xining-Chengdu Railway project. Its main span was scheduled for closure by the end of August.

The tragedy underscores growing concerns about safety standards at major infrastructure projects in China.