Police were carrying out a series of raids this morning against men involved in the sexual exploitation of teenage girls.
The operation follows a three-month investigation involving around 100 detectives, according to Greater Manchester Police (GMP).
Addresses in Longsight, south Manchester, Salford and Clayton were being targeted.
The victims are teenage girls living in the Stockport area.
Police say further details will be released later today.
A spokesman said: "This morning, 14 June 2011, a joint operation by officers from GMP's Major Incident Team (MIT) and Stockport Division is making a number of arrests in connection with an investigation into organised crime groups.
"Focusing chiefly on child sexual exploitation, the investigation involves around 100 detectives and is one of the largest ever carried out by the Serious Crime Division.
"The arrests are the result of a three-month inquiry into the sexual exploitation of a number of teenage girls from Stockport by men.
"Addresses in Longsight, south Manchester, Salford and Clayton are being targeted this morning.
"More details of the arrests will be released later this morning."
It is understood that officers are investigating reports of men involved in supplying alcohol and drugs to under-age girls at sex parties.
Six men have so far been arrested at addresses in Cheetham Hill, Fallowfield, Levenshulme, Moss Side and Chorlton-on-Medlock, all Manchester or Salford.
The suspects are being held in custody on suspicion of trafficking within the UK for the purposes of sexual exploitation.
Assistant Chief Constable Terry Sweeney, of GMP, said: "I hope today's action shows people in Greater Manchester that the issue of sexual exploitation is one that we take extremely seriously.
"This is the largest ever operation carried out by the Major Incident Team and we have had dozens of detectives, including a team from Stockport, working on this investigation.
"It is believed there could ultimately be more victims in this case and officers now want to hear from anyone else who thinks they may have been sexually exploited.
"I want to reassure the people of Greater Manchester that we have a number of operations currently targeting this kind of criminal behaviour.
"I cannot go into details as that could jeopardise the operations, but people need to know this issue is at the top of GMP's priorities.
"We work closely with local authorities, and other organisations such as Barnardo's, to address the specific issue of adults befriending and grooming younger people for sex."