Rotten ceiling beams and persistent rain have been identified as contributors to the collapse of a tunnel last month at a hydropower scheme in Vietnam.

According to local media, Vo Nhat Thang, chairman and general director of Long Hoi Electricity Construction and Investment JSC, said that wooden ceiling molds used during construction of the Da Dang-Da Chomo hydropower scheme had decayed, allowing rocks and concrete to fall. He also said that over a month’s worth of rain helped lead to the collapse, while also mentioning poor geology at the project

"The geological formation in this area is very complicated. Two experienced contractors – Lung Lo and Vinaconex – began work on the tunnel, then quit for that reason," he said.

The collapse occurred on 16 December, trapping 12 workers inside. They were successfully freed by rescuers on 19 December.

Further investigations at the project are ongoing.