The Internet Watch Foundation (IWF) received 392,660 reports of possible abuse images on websites in 2023, of which 275,655 were found to contain such material.
Of those, 107,615 (39 per cent) were found to contain images of children under 10, up from 64,735 pages out of 255,580 (25 per cent) in 2022.
Each of the pages can contain hundreds or thousands of images of abuse.
A total of 254,070 (92 per cent) of the pages reported in 2023 featured what is classed as self-generated pictures or videos, where children are tricked or forced into taking obscene images of themselves.
About a fifth of the self-generated material was in the worst category, the IWF said.
In the previous year, 199,360 pages out of the 255,580 were found to contain child abuse material contained self-generated images (78 per cent), of which 32,871, or 16 per cent, were in the worst category.
Chief executive of the IWF, Susie Hargreaves, said: "The imagery extorted or coerced from primary school-aged children is now finding its way onto the most extreme, dedicated child sexual abuse sites in shocking numbers.
"What starts in a child's bedroom, over a webcam, is shared, traded and harvested by committed and determined sexual predators. The IWF is seeing the results in unprecedented numbers. These criminals are ruthless."
She hit out at plans by Meta to bring in end-to-end encryption on Facebook Messenger.
In 2022, the tech giant passed more than 20 million reports of users potentially sharing images of children being sexually abused to a US helpline.
"It is incomprehensible that Meta is deciding to look the other way and offer criminals a free pass to further share and spread abuse imagery in private and undetected.
"Decisions like this, as well as Apple opting to drop plans for client-side scanning to detect the sharing of abuse, are baffling given the context of the spread of this imagery on the wider web.
"Children are falling victim like never before. There really has never been a worse time to be a child on the internet, and Meta's decision to bring in end-to-end encryption appears to be willfully making this worse, not better, ignoring the evidence, and rewarding criminals with safe spaces at children's expense."
Apple has been approached for comment.
Security Minister Tom Tugendhat said: "This alarming report clearly shows that online child sexual abuse is on the rise, and the victims are getting younger.
"And yet, despite warnings from across government, charities, law enforcement and our international partners, Meta has taken the extraordinary decision to turn its backs on these victims, and provide a safe space for heinous predators.
"The decision to roll out end-to-end encryption on Facebook Messenger without the necessary safety features, will have a catastrophic impact on law enforcement's ability to bring perpetrators to justice.
"It isn't too late to work with us to keep children safe online. As Meta begins to implement default end-to-end encryption in the UK, they can and must ensure that robust safeguards are implemented at a time when children are at a greater risk online than ever before."
Sir Peter Wanless, NSPCC chief executive, said: "It is alarming that the amount of child sexual abuse material online has continued to rise and is particularly worrying that increasing numbers of primary school-aged children are being targeted, groomed and coerced into sharing images of their own abuse.
"Amidst such unprecedented levels of child abuse, tech firms should be preparing for the Online Safety Act to come into force by addressing the way their sites put children at risk of sexual abuse.
"Instead, Meta is rushing out end-to-end encryption on its messaging services in the UK which will blindfold itself and law enforcement to the child sexual abuse taking place on its platforms and the young victims who desperately need help.
"Meta's executives can still pause the rollout of end-to-end encryption to allow regulators and experts to scrutinise their risk assessments and work with the company to ensure they do not undermine efforts to identify and disrupt child abuse.
A Meta spokesperson said: "Encryption helps keep people, including children, safe from hackers, scammers and criminals.
"We don't think people want us reading their private messages, so we have spent years developing robust safety measures to prevent, detect and combat child abuse while maintaining online security.
"Our recently published report detailed these measures, such as restricting over 19s from messaging teens who don't follow them and using technology to identify and take action against malicious behaviour.
"We routinely provide more reports to the National Centre for Missing and Exploited Children than others, and given our ongoing investments, we expect that to continue."
-- BERNAMA
