Swiss police officers stand beside of mock gates of the NEAT Gotthard Base Tunnel inside the event hall for the upcoming opening ceremony near the town of Erstfeld, Switzerland May 31, 2016. The celebrations of the opening of the Gotthard Base Tunnel will start on June 1, 2016. With a length of 57 km (35 miles) crossing the Alps, the Gotthard Base tunnel is the world's longest train tunnel. (Photo by Arnd Wiegmann/Reuters)

Artists perform during the opening show directed by German director Volker Hesse, on the opening day of the Gotthard rail tunnel, at the fairground Rynaecht at the northern portal in Erstfeld, Switzerland, Wednesday, June 1, 2016. The construction of the 57 kilometer long tunnel began in 1999, the breakthrough was in 2010. After the official opening on June 1, the commercial operation will start in December 2016. (Photo by Ruben Sprich\Pool Photo via AP Photo)

A masked reveller hangs from an inflatable balloon during the first day of the carnival in Venice, Italy, January 23, 2016. (Photo by Manuel Silvestri/Reuters)

A worker works at a plant of Hyundai Motor in Asan, South Korea, January 27, 2016. (Photo by Kim Hong-Ji/Reuters)

Men pull as a boy stands on a soap cutter in a soap factory in Idlib province, Syria January 30, 2016. (Photo by Ammar Abdullah/Reuters)

Revellers parade for Gavioes da Fiel samba school during carnival in Sao Paulo, Brazil, February 6, 2016. (Photo by Paulo Whitaker/Reuters)

A worker collects rubber sap at a farm in Songon village, north of Abidjan, February 3, 2016. (Photo by Luc Gnago/Reuters)

Paramilitary policemen carry tyres as they take part in a training session in Zhangye, Gansu Province, China, March 1, 2016. (Photo by Reuters/Stringer)