Zhoushan side of the Jintang Undersea Tunnel. [Photo provided to chinadaily.com.cn]

Construction of the world's longest undersea high-speed railway tunnel has reached a significant milestone, as the "Dinghai" Shield Machine surpassed the 5,000-meter mark in the Jintang Undersea Tunnel.

At the Zhoushan site of the Ningbo–Zhoushan Railway project, Friday's breakthrough indicated that about 80 percent of the 6,270-meter shield section on the Zhoushan side has been completed.