A restaurant in northern China’s Shanxi province collapsed Saturday morning, killing 29 people and injuring 28 more, according to state broadcaster CCTV.

The incident occurred in the prefecture-level city of Linfen during a gathering organized by a local resident to celebrate his 80th birthday. He had stepped outside for a few moments when he saw the roof of the first-story banquet hall cave in. He survived the collapse, but his wife who remained inside the structure was killed.

At least three children are among the deceased, according to reporters with Sixth Tone’s sister publication The Paper who were at the scene.

The collapsed banquet hall was built in a courtyard between two other buildings by Linfen locals a few years ago. The roof was made with relatively cheap and lightweight — and generally more fragile, compared with reinforced concrete — building materials called prefabricated structural panels. Such panels were once commonly used for construction projects in rural areas.

However, the cause of the collapse is unclear for now. Shanxi’s provincial government has assembled a “major accident investigation team” to look into the incident.

Contributions: Yan Hailong; editor: David Paulk.

(Header image: An aerial view of the rescue operation underway at the site of a collapsed restaurant in Linfen, Shanxi province, Aug. 29, 2020. Wu Junjie/CNS/People Visual)