Switzerland's main north-south road axis through the Alps – the Gotthard - was closed on Wednesday, following a rockslide, which crushed a car killing two people.
Traffic jams of up to 15 kilometres were reported on either side of the San Bernardino Pass, the main alternative route linking northern Europe and Italy.
Lorries were temporarily banned from using either route, which meant they had to skirt the country altogether, or transfer their freight to rail.
It was not clear for how long the Gotthard would be closed. Officials said the route would certainly not be opened again before Friday.
The rock fall occurred early on Wednesday morning on the northern approach to the Gotthard tunnel. Huge boulders rolled on to the A2 motorway hitting German-registered car, and killing its two occupants, who have yet to be identified.
"We know that there were two people inside and that it was a German car," said Karl Egli, spokesman for the local police. He added that the car had burst into flames and was completely destroyed.
Closed to traffic
Police were redirecting north- and south-bound traffic eastward to the San Bernardino Pass and said they expected the A2 route to remain closed on Wednesday at least, and possibly for longer.
By Wednesday afternoon, traffic jams of up to 15 km had formed on the north and south sides of the San Bernardino Pass. They later cleared, but police were expecting more congestion ahead of the Pentecost weekend.
Geologists are currently in the area assessing the possibility of further rock falls. It is thought the slide may have been triggered by the heavy rain and snowfalls in recent days.
swissinfo with agencies
Swiss transport policy aims to move freight traffic off the roads and motorways and on to the railways, particularly for freight traffic transiting the country.
Two new rail tunnels are currently under construction: the 57-km Gotthard (which will be the longest in the world) and the 35-km Lötschberg. They are scheduled for completion in 2012 and 2007 respectively.