The 35.4-mile-long, 6 billion pounds Gotthard Tunnel will speed up railway connections between northern Europe and Italy, the Telegraph reported.
Huge boring machines have been tunnelling through the mountains from two directions: in the north from Erstfeld, near Lake Lucerne, and in the south from Bodio, near Switzerland's border with Italy.
Only six feet of rock now separate the two tunnelling teams and the final breakthrough is scheduled for October 15.
According to the company in charge of the project, AlpTransit Gotthard AG, the machines cut into the rock at the rate of 50-65ft a day, grinding slowly through the mountain's base "like millipedes".
They performed about 60 percent of the tunnelling work, with the rest done by blasting with explosives.
The workforce has been described as an "underground Babylon", with around two-thirds of the workers being Austrian and Italian, and the rest German, Turkish, Spanish, Portuguese and the Balkans. Only a few are Swiss.
Once the excavation is completed, work will begin on laying down railway tracks, signals and safety systems.
There will be emergency stop stations every 12.5 miles where passengers could be evacuated in the event of a train crash or fire.
The tunnel is scheduled to open in December 2017, with trains travelling at 155mph, shortening the travelling time between Milan and Zurich by one hour. (ANI)