As IM says, speak to your usual vet about the practice's emergency protocol. Many vets have an on-call rota for after hours emergencies.
Additionally, the University of Zürich's Tierspital is the metro area's hospital, available for emergencies 24/7.
https://www.tierspital.uzh.ch/de.html
Always call first!
by the way, the Tierspital is also the place you might be referred to for specialist care. It's one of the premier veterinary institutes in Europe.
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I am about a hour away from the Tierspital, so even when I suspect their expertise might be needed in an emergency, I go first to my own clinic in the neighborhood so that they can get my dog stabilized. Then if it is decided that a transfer to the Tierspital is needed, my clinic arranges that, and off we go.
Most Zürich metro area vets work with the Tierspital, cooperation is excellent.