China's longest undersea subway tunnel was completed on Saturday after 728 days, 70 days ahead of schedule, in northeast China's port city of Dalian. The Dalian No. 5 subway line is designed to be 24.484 kilometers long, with 18 stations. The length of the tunnel boring machine zone is 2,882 meters, with 2,310 meters running through the sea. The No. 5 subway line is expected to be operational by the end of 2022.