Dozens (or dozens of people) were run over by a van in a Spanish city.
In "jornalese" (that is a jargon-ish, or slang, whichever you wish) it could be: Dozens were run over by van in City of Spain.
Jornalese is the choice of words they use in headline news, for example, to hook the reader. Yet being as terse as they can be at the same time.
And yes, "dozens" is the word to our "dezenas" in such situation. Tens would be used when we can, more or less count in groups of ten, in headlines emotionally charged, "dozens" is the way. But when translating back to Portuguese, use "dezenas".