"Train services have been halted since around 4.30pm on the Saint Gotthard line after a landslide" near central Switzerland's Gurtnellen, Swiss Federal Railways (SBB) said in a statement.
"The interruption will last several days," it said, adding that the incident occurred "near where another landslide happened in June".
Unlike that previous incident, in which a rail worker was killed, no one was hurt in the latest landslide in which 150 cubic metres of rocks fall onto the tracks, SBB said.
No trains were passing at the time of the landslide and early warning systems had functioned properly to halt all services in time, the rail operator said.
While the line stays closed, passenger and freight trains are to travel via the Simplon tunnel — another major axis.
On average, 120 freight trains use the Saint Gotthard line every day.