Construction of the New Rail Link through the Alps (NRLA) in Switzerland which comprises Gotthard and Ceneri Base Tunnels, achieved a major breakthrough in April with the excavation of total access passage of the Gotthard Base Tunnel.

Of the total 151.8 km of access passages, shafts and main tunnels, 151.8 or 100 per cent have already been excavated at Gotthard Base Tunnel, according to work status update released on the project's official website on Wednesday.

The work status at Ceneri also achieved a breakthrough last month as of the total of 39.78 km, 19.19 km or 48.3 per cent of excavation work was accomplished.

"In mid-April 2012, breakthrough took place at the Wysshus underpass in Altdorf/Rynächt. On 2 April, 2012, construction began of the of the railway systems building at Sedrun. At the end of April 2012 at Sigirino, around 4 km of the final invert had been concreted. Work on the invert continues in both directions," AlpTransit, a subsidiary of Swiss Federal Railways (SFR), which is contructing NRLA, said in a statement.

Gotthard and Ceneri Base Tunnels will together form the world's longest train tunnel, surpassing the Seikan Tunnel in Japan. The new fast and efficient railway link is aimed at cutting passenger travelling time substantially, which is made possible by the construction of straight passages with wide curves.

"The new Gotthard route is a high-speed rail link. Passenger trains can traverse its almost 60 kilometres length at maximum speeds of up to 250 kilometres per hour. This is enabled by the straight route with no tight curves and no level crossings on the overground sections."

"The new railway link crosses the Alps with minimal gradients and wide curves. At only 550 metres above sea level, the highest point is no higher than the city of Berne."

Opening of the Gotthard Base Tunnel is scheduled for December 2016, while for Ceneri Base Tunnel, the opening is scheduled for December 2019.

Check out some of the recent breakthrough pictures of construction work at Gotthard and Ceneri Base Tunnels: