First, clasify "emergency march" because that can be speeding or slowing down. In the case of slowing down, your are correct. In the case of speeding, you are not.
Around here you can put your vehicle in emergency march, in cases of...emergencies and if it doesn't endanger others.
No vehicle (this includes police cars) can go over the speed limit. Only special vehicles under very specific circumstances can go over the speed limit in specific situations.
Speeding (and going below the slowest possible limit) causes many deaths.
I'm sorry, I didn't realise you were up-to date on the laws in Portugal... Laws differ from state to state within the US, never mind from country to country.
In some places (dependant on circumstances) it is legal to exceed the posted speed limit.