BEIJING (AP) — A scaffolding collapse at one of Beijing’s most prestigious high schools on Monday killed 10 construction workers and injured four others, officials said.

The accident occurred at the start of the school day at Tsinghua High School in the city’s northwest, but did not affect any classrooms or other buildings used for instruction, according to a statement from the Beijing municipal propaganda bureau. It said the injured were in stable condition.

A high school official with the surname Jiang said all of the victims were constructing a gymnasium at the school, which is affiliated with one of China’s top universities, also called Tsinghua. He said no teachers or students were hurt.

Relatives of the victims waited outside the school gates to be allowed in. A teary-eyed man said his cousin had been working there and that another worker at the construction site had called to tell him there had been an accident.

Another man, Wang Zhiquan, said his nephew Chen Haijun, 42, a migrant worker from Heilongjiang province in China’s northeast, had been killed.

He told reporters he wanted to see the site and seek proper compensation because Chen was the sole breadwinner for his family, including two ill parents and two children.

The official Xinhua News Agency said an initial investigation found that steel bars used to reinforce concrete had collapsed and caused the accident. It said police had detained several people, but gave no details about their identity.