BEIJING—Workers were about 1.1 kilometers (0.7 miles) from the entrance to the tunnel when a strange noise was heard and material started falling from the top of the tunnel, Yan Dawu, the deputy general manager of the construction company, said at a news conference.
An evacuation was ordered, but water gushed in and 14 people were unable to get out, Yan said.
The area where they were working is under a reservoir.
In March, two workers died in another part of the tunnel when a protective wall collapsed and they were hit by falling stones, according to a notice from the Zhuhai emergency management department.
Zhuhai is a coastal city near Macao at the mouth of the Pearl River delta.