A section of the A9 autoroute in Valais has been closed to trucks and a lane closed for cars after part of the road collapsed.
A hole over a meter across opened up between Sierre and Sion - and police admit they have no idea why.
On worries heavy vehicles may cause more problems, any over 3.5 tonnes have to take a detour.
Engineers are now trying to figure out the reason for the collapse.