Swiss Federal President Johann Schneider- Ammann, right, speaks with German Chancellor Angela Merkel, left, on the opening day of the Gotthard rail tunnel, at the fairground Rynaecht at the northern portal in Erstfeld, Switzerland. [Photo/Agencies]

High-speed trains will whisk passengers in 17 minutes through the tunnel, a passage that took days until the first Alpine rail route opened in 1882. Around 260 freight trains and65 passenger trains can traverse the two-tube tunnel daily once final testing ends later this year.

The Swiss threw an opening party that drew the leaders of all its neighbouring countries in a show of European solidarity.

Swiss President Johann Schneider-Ammann said he would gently press German Chancellor Angela Merkel, Italian Prime Minister Matteo Renzi and French President Francois Hollande to compromise in a standoff over Swiss plans to launch unilateral curbs on EU immigration.

"We will come closer personally and that is decisive," he told reporters, adding talks would resume in earnest after Britain's June 23 vote on whether to quit the EU.