The EU has told TikTok it must change its "addictive design" or face heavy fines, after it found the video sharing platform had breached its online safety rules.

It follows an investigation which began in February 2024 into the Chinese-owned app by the European Commission.

In its preliminary findings, the Commission said TikTok did not "adequately assess" how features like autoplay could harm the wellbeing of its users, including children, and said it failed to implement measures to mitigate the risks.

A TikTok spokesperson told the BBC the findings presented a "categorically false and entirely meritless depiction of our platform" and it planned to challenge them.

The platform has been invited to respond to the EU's findings. Depending on the outcome of this step, the Commission could fine TikTok up to 6% of its total global annual turnover - estimated to be in the tens of billions.

EU tech chief Henna Virkkunen told reporters if TikTok wanted to avoid being fined, it would have to "change the design of their service in Europe".

The Commission gave several suggestions for actions the platform could take, including implementing "screen time breaks" when people are using it at night and changing its algorithms, which feed users personalised content.

It also suggested TikTok disable so-called "infinite scroll", which allows people to quickly cycle through millions of videos on the platform.

"The Digital Services Act makes platforms responsible for the effects they can have on their users," Virkkunen said.

"In Europe, we enforce our legislation to protect our children and our citizens online."

Social media analyst Paolo Pescatore said it was a "reality check" for TikTok - and a "warning shot" for every social media platform.

"The market is shifting from 'maximise engagement' to 'engineer responsibility' - and regulators now have the tools to enforce it," he said.

Meanwhile, Professor Sonia Livingstone at the London School of Economics said while TikTok had introduced some tools to improve the online safety of its users, it was not enough to comply with the guidelines set down by the EU.

"Young people are calling for such changes," she said.

"They are frustrated that the platform does not prioritise their wellbeing over profit."