About 350 victims have reported child sexual abuse within UK football clubs, police chiefs have said.
The National Police Chiefs' Council said a "significant number of calls" had been received after several former players alleged past abuse by coaches.
Its figures are also based on details from existing investigations as well as referrals from a new NSPCC helpline.
Greater Manchester Police said it was investigating reports from 35 people, and had identified 10 suspects.
Assistant Chief Constable Debbie Ford said the force had received calls on a daily basis from victims as well as people with concerns.
"We are currently in the process of speaking to victims in person and providing them with specialist support," she added.
Meanwhile, Devon and Cornwall Police and Warwickshire Police have become the latest forces to confirm they are investigating claims.
The 17 forces looking into allegations of historical child sex abuse in football also include the Metropolitan Police, North Yorkshire Police, Police Scotland and Cheshire Police.
The NSPCC says more than 860 people have called its dedicated football hotline, set up a week ago.
Within the first three days of it launching, the charity made more than 60 referrals to a range of agencies across the UK.
That was more than three times as many referrals as in the first three days of the Jimmy Savile scandal, the charity added.
The phone line is available 24 hours a day on 0800 023 2642.
The Football Association has announced an internal review and a number of football clubs are conducting their own inquiries.
'Significant' police response
Outlining the police action to date, NPCC lead for Child Protection, Chief Constable Simon Bailey said the number of victims was "an indicative figure only", and with information still being collated numbers could change.
He said some of the cases being investigated had come from information supplied by forces across the UK to Operation Hydrant, set up in 2014 to oversee investigations into historical child sex abuse concerning prominent people.
"We are working closely with the Football Association to ensure the response to this significant and growing number of victims, at all levels of football, is co-ordinated effectively," he added.
"We continue to encourage those who have been the victim of child sexual abuse to report it, regardless of how long ago the abuse may have taken place."
He said all reports would be treated "sensitively and seriously".
The former Newcastle United footballer David Eatock has become the latest to say he was abused by coach George Ormond.
He told the BBC's Victoria Derbyshire show he had been groomed by Ormond, later to be jailed for six years, between the ages of 18 and 21.
Mr Eatock, now 40, was not part of the court case that saw Ormond convicted in 2002 of assaulting seven boys, but he has now filed a complaint to police.
Northumbria Police said it had launched Operation Tide into non-recent child abuse at Newcastle United.
The force said it had received "a number of reports" and club officials have met police.
New England football manager Gareth Southgate said a former teammate was among those to have spoken of abuse.
At his first news conference as England manager, Southgate revealed he had played alongside one of the footballers who has spoken out about being sexually abused in their youth - although he did not identify him.
Asked if he had been aware of any abuse going on, he said: "The reality of that, as they have said, is that they [abuse victims] haven't felt able to speak about that until this moment, and that's completely understandable."
There had been "enormous strides" made in protecting young players, he told reporters.
Police forces investigating allegations:
- North Wales
- North Yorkshire
- Greater Manchester
- Police Scotland
- Avon and Somerset
- Devon and Cornwall