Workers pose for a group photo inside the tunnel boring machine "Dinghai" in celebration of the machine exceeding a tunneling mileage of 5,000 meters in Zhoushan, East China's Zhejiang province, Nov 28, 2025. [Photo provided by China Railway 11th Bureau Group]

China's self-developed tunnel boring machine "Dinghai" exceeded a tunneling mileage of 5,000 meters on Nov 28 at the Jintang undersea tunnel between cities of Ningbo and Zhoushan in East China's Zhejiang province.

The milestone marks the completion of over 80 percent of the tunneling workload in Zhoushan section of Jintang undersea tunnel.

The tunnel, stretching 16.18 kilometers, is an crucial part for the Yongzhou (Ningbo-Zhoushan) high-speed railway, and is set to be the world's longest undersea railway tunnel upon completion.