Here are some Portuguese phrases and exclamations for use in emergencies and other difficult situations. Hopefully you won't need to use them!

cuidado!be careful!
atenção!watch out!
por favor ajude-meplease help me
chame uma ambulância!call an ambulance! (to one person)
chamem uma ambulância!call an ambulance! (to more than one person)
houve um acidentethere's been an accident
roubaram-me a carteiramy wallet has been stolen
pára ladrão!stop thief!
chame a polícia!call the police! (to one person)
chamem a polícia!call the police! (to more than one person)
estou perdidoI'm lost (for a man)
estou perdidaI'm lost (for a woman)
estamos perdidoswe're lost (for a group of men or a mixed group)
estás bem?are you ok? (familiar)
está bem?are you ok? (polite)