China will complete its first undersea tunnel for high-speed trains by 2025, connecting the Zhoushan Islands in eastern Zhejiang province with the mainland, according to local authorities.

Sources from the Zhoushan development and reform commission said progress has been made on the first-phase feasibility study for the massive project, which was initiated in June last year. Construction is expected to begin next year.

On Nov 19, a feasibility evaluation for the new railway was made in Beijing, a significant step before construction begins.

The project, connecting the city of Ningbo with the island city of Zhoushan, will be 70.92 kilometers in length, including an undersea tunnel of 16.2 kilometers linking Beilun in Ningbo with Zhoushan's Jintang Island, according to the plan. The Ningbo section will be 23.77 km long; the Zhoushan section will be 47.15 km.

Trains will run at 250 kilometers per hour, cutting the trip between the cities from 1.5 hours to less than 30 minutes.

A consultation meeting in Zhoushan, organized by Zhejiang's transportation department earlier this year, said the rail link will greatly ease congestion on the current Zhoushan Cross-Sea Bridge, which opened in December 2009 after an investment of 13 billion yuan ($1.9 billion).

The Ningbo-Zhoushan railway is expected to present some complex engineering difficulties, according to the local Ningbo Daily.

China has 25,000 km of high-speed railway lines across the country, accounting for more than 60 percent of the world total.