This tunnel will revolutionise the European freight transport.
The grand opeming ceremony is attended by the German Chancellor Angela Merkel, French President Francois Hollande and Italy's Prime Minister Matteo, reported the BBC.
The Gotthard Base Tunnel, hewn through mountain rock and providing a high-speed rail connection between northern and southern Europe, will become one of the main rail links across the Alps and the longest in the world, with a length of about 57.1 km.
Visitors can travel through the world's longest railway tunnel in special trains on this weekend, the Swiss government source said.
The commercial services for the tunnel are scheduled to begin from December 2016. The construction of the tunnel began in 1996, with the total cost of 9.8 billion Swiss francs, or $10.3 billion.