A woman was sexually assaulted by a group of teenagers wearing Halloween masks, police said.
The 22-year-old victim was approached by four youths who were wearing Scream-type masks before she was dragged to the ground and sexually assaulted.
The woman managed to fight them off and raised the alarm.
Police said one of the teenagers was chubby and in his early teens while another was tall and wearing white trainers. The attackers were wearing dark clothing .
Greater Manchester Police said the woman was walking along Sunningdale Road in the Haughton Green area of Denton on Friday night when she was attacked .
Superintendent Neil Evans said: "This young woman has suffered a traumatic ordeal at the hands of four individuals who were dressed in Halloween-type masks.
"She was pushed to the floor and sexually assaulted, leaving her in a state of total shock, and clearly she is extremely distressed.
"Anyone who has been a victim of sexual assault will know just how frightening it must have been for this victim, and given the offenders were wearing masks designed to be scary means it must have been a truly harrowing and scary few minutes for this woman."
He added: "The purpose of this appeal is not to unduly alarm the community but it is important we let people know what has happened so they can both be vigilant and help us track down these cowardly offenders.
"If you know of anyone who might be involved, then please call us.
"If you are a parent and you know your child went out with friends dressed in these type of masks and you have suspicions then, please, do the right thing and call us.
"This woman has suffered a terrible ordeal and we need, for her sake and the wider community, to catch the culprits.
"We are conducting a number of inquiries in the local community and I want to assure people we will do everything we can to find those responsible."
Police are appealing for anyone who has information about the assault to call police on 101 or Crimestoppers, anonymously, on 0800 555 111.