The regulator, Ofcom, has laid down more than 40 practical measures for tech firms to meet their duties under the UK's Online Safety Act, a new law that imposes legal responsibilities on platforms to protect children.

"Children in the UK will have safer online lives, under transformational new protections," Ofcom said.

The measures will apply to websites and apps used by children in areas such as social media and gaming and are aimed at preventing minors from encountering harmful content relating to suicide, self-harm, eating disorders and pornography.

Tech firms must also protect children from misogynistic, violent, hateful or abusive material, online bullying and dangerous challenges.

"These changes are a reset for children online," said Ofcom Chief Executive Melanie Dawes.

"They will mean safer social media feeds with less harmful and dangerous content, protections from being contacted by strangers and effective age checks on adult content," she added.

"If companies fail to act they will face enforcement."

Rule-breakers face fines of up to pound18 million ($22.5 million) or 10 percent of their revenue.

Tech firms will be duty bound to configure algorithms to filter out harmful content from children's feeds, implement effective age checks and "quickly tackle harmful content when they become aware of it".

Children should also be able to indicate what content they do not like, to accept or decline group chat invitations, to block accounts and to disable comments on their own posts.

Providers of services likely to be accessed by children in the UK now have until July 24 to complete an assessment of the risk their service poses to children.

From July 25, they should apply the safety measures set out by Ofcom, according to the measures.

"If companies fail to comply with their new duties, Ofcom has the power to impose fines and -- in very serious cases -- apply for a court order to prevent the site or app from being available in the UK," added the regulator.