Opening soon: The world's longest railway tunnel

The world's longest tunnel, the Gotthard Base Tunnel, is set to open in early June in Switzerland.

It will connect Europe's high-speed rail network and play a great part in protecting the Alps from erosion.

When it opens, the Gotthard will surpass the 53-kilometre Seikan tunnel in Japan to become the longest rail tunnel on the planet.

See also: Road tunnel to be built under Stonehenge?

At 50 kilometres, the Channel Tunnel between France and the UK will be bumped to third.

However Austria's delayed Brenner Tunnel could take second place when it opens in about a decade at an estimated length of 55 kilometres, said AFP.

With 2,300 metres of rock above it, the Gotthard will also be the world's deepest rail tunnel, says construction company Alp Transit.