One was released without charge but the other five remain in custody tonight said a spokesperson for Humberside Police.
Four were detained on suspicion of possession of a controlled substance and one on suspicion of possession of a controlled substance with intent to supply.
ACC Scott Young said: “We know that this is something that is causing concern for a lot of people – and we’re also concerned.
“It’s not what we want to see in our city and it’s something we have been working with other organisations across Hull to tackle for some time.
“Up until recently, the main issues we have had reported to us have been around anti-social behaviour and homelessness, which are complex and challenging problems which require input from a number of organisations, including Hull City Council, health and social care groups and our teams.
“However, that picture has now changed to include reports of people openly dealing drugs in the city centre and that’s something that we will not accept.
“Wherever we have evidence of this kind of behaviour, we can and do take action and I would appeal to people to keep that information coming in to us."
He asked if anyone has information on such activity to call 101 or 999 in an emergency.”