Liechtenstein's Prime Minister Adrian Hasler addresses guests during the opening ceremony of the NEAT Gotthard Base Tunnel, the world's longest and deepest rail tunnel, in Pollegio, Switzerland June 1, 2016. [Photo/Agencies]

Switzerland opened the world's longest and deepest rail tunnel through the heart of the Alps on Wednesday in an engineering marvel hailed as a symbol of European unity at a time of increasing fragmentation.

The 57.1-km (35.5 mile)-long Gotthard Base Tunnel, 17 years under construction, is part of a 23 billion Swiss franc ($23 billion) infrastructure project to speed passengers and cargo by rail under the mountain chain dividing Europe's north and south.

Typically Swiss, the Gotthard tunnel that federal transport office director Peter Fueglistaler called "a masterpiece of timing, cost and policy" came in on schedule and on budget.