If parents give a spank to their child, this is considered violence and as such frown upon - and in some countries simply a crime under the law.
In my observation, parents who don't want to spank often resort to things like grounding, canceling birthday party, sending the child to bed without dinner, shaming him/her in front of his/her friends, holding announced gifts etc. for punishment.
Is it correct to consider the latter as "non-violent" forms of punishment ? They certainly amount to psychological violence, and the pain they generate can be greater and more long-lasting than a spank, plus a spank is usually delivered right away after the child's bad behavior, while things like grounding or holding a gift are supposed to "teach the lesson" even long after the child already forgot the link between that and his/her bad behavior so there is the risk that the child will simply feel that the parents are "evil" to him/her for no reason, although not physically violent.
On the other hand a physical punishment doesn't exactly sound like a very thought-through way to go, plus many parents just feel too bad doing that and simply cannot do that.
I'm talking about age 4-5.
ADDED: I'm new here and I just realized that it's very important to keep the question as one question, which I think makes a lot of sense. So the question here is just the one in the title and I just removed the last paragraph because it contained a separate question. If I come to the conclusion that non-physical punishments must still be considered violence I will perhaps post a new question about which one of those two types of violence is most harmful. Sorry for the confusion.