careful of pickpockets in heavily crowded areas and on public buses and trains although '''it's not very common to happen''' as other European cities like Barcelona, Paris, Madrid etc.Travelling by Bus or Metro it's safe and one of the best ways to go from a place to another since both have great conditions.
Porto is generally a safe place to be if you take normal precautions like walking in well-illuminated streets at night.
One part of Porto, near the Tourist Information Office between the cathedral and the steps to the small church, often has drunk people that could possibly be trouble. There's no reason for alarm because many of them are inoffensive, but it is best to use some caution
like elsewhere. If you take the main road from the bus station to the cathedral and tourist information center, walk back to the bus station after you 're done and then walk from there to the other sites. Avoid the shortcut from the tourist information center down stairs because near there are many incidents there.
Call 112 if you have an emergency.