Two boys were among those arrested in dawn drugs raids across North Manchester and Salford.
Police are cracking down on heroin dealing, particularly in Cheetham Hill and Crumpsall.
In total, 17 were arrested in raids on 18 properties in the area.
The boys, aged 15 and 17, were arrested on suspicion of being concerned in the supply of class A drugs, along with nine other men, aged 18-44.
Six other men were arrested on suspicion of other offences.
A 37-year-old man was arrested on suspicion of obstructing a police officer, a 26-year-old man was arrested on suspicion of theft and a 36-year-old man was arrested on suspicion of possession of drugs.
Three more were arrested for immigration offences.All remain in custody, being questioned by police.
Community-led intelligence told police heroin was being bought and sold in broad daylight on the streets.
Greater Manchester Police Superintendent Vanessa Jardine said: "The supply of drugs can blight our communities but today's action is aimed at ridding our streets of this nuisance.
"Community-led intelligence has told us that there has been issue developing of dealing of heroin in particular in Cheetham Hill and Crumpsall, including reports of drugs being bought and sold in broad daylight.
"We also have intelligence to suggest there are tensions between rival gangs of drug dealers and that a 'turf war' is developing.
"These issues cannot be tolerated.
"It is a priority for Greater Manchester Police to tackle the threat of organised crime, and to increase confidence in policing.
"Today we have shown that we are committed to these priorities.
"Not only do drugs fuel many other crimes such as burglary, robbery and vehicle crime, they are also a major driving force behind organised crime groups and today we have hit them where it hurts by disrupting their income.
"I hope we have also increased confidence in policing by proving to the vast majority of decent, law-abiding residents of Cheetham Hill and Crumpsall that we listen to their concerns and act on the information that they give us.
"The fact that more than 20 local people, be they residents, councillors or businesspeople, came to our 5.30am briefing shows that we are all working together to root out this problem.
"Let today be a stark warning to anyone involved in drugs activity that not only will they face the full force of the law, but through Proceeds of Crime Act legislation, they will also end up out of pocket.
"Residents will also notice an increased police presence today, as leaflets will be dropped through letterboxes to explain what is happening, and drugs workers are also on hand to support addicts affected by today's operation."