SYDNEY, Dec 10 (Reuters) - Australia at midnight (1300 GMT) on Wednesday became the first country in the world to ban social media for children under 16, blocking them from platforms including TikTok, Alphabet's GOOGL.O YouTube and Meta's META.O Instagram and Facebook.

Ten of the biggest platforms were ordered to block children or be fined up to A$49.5 million ($33 million) under the new law, which was criticised by major technology companies and free speech campaigners, but praised by parents and child advocates.

The ban is being closely watched by other countries considering similar age-based measures as concerns mount over the effects of social media on children's health and safety.

"While Australia is the first to adopt such restrictions, it is unlikely to be the last," Tama Leaver, a professor of internet studies at Curtin University, said.

"Governments around the world are watching how the power of Big Tech was successfully taken on. The social media ban in Australia ... is very much the canary in the coal mine."

BAN HAS SEEN LAWMAKERS TAKE ON TECH INDUSTRY

The rollout closes out a year of speculation about whether a country can block children from using technology that is built into modern life.

And it begins a live experiment that will be studied globally by lawmakers who want to intervene directly because they are frustrated by what they say is a tech industry that has been too slow to implement effective harm-minimisation efforts.

Governments from Denmark to Malaysia - and even some states in the U.S., where platforms are rolling back trust and safety features - say they plan similar steps, four years after a leak of internal Meta documents showed the company knew its products contributed to body image problems and suicidal thoughts among teenagers while publicly denying the link existed.

BEGINNING OF THE END

Though the ban covers 10 platforms initially, the government has said the list will change as new products appear and young users switch to alternatives.

Of the initial 10, all but Elon Musk's X have said they will comply using age inference - guessing a person's age from their online activity - or age estimation, which is usually based on a selfie. They might also check with uploaded identification documents or linked bank account details.

For the social media businesses, the implementation marks a new era of structural stagnation as user numbers flatline and time spent on platforms shrinks, studies show.

Platforms say they don't make much money showing advertisements to under-16s, but they add that the ban interrupts a pipeline of future users. Just before the ban took effect, 86% of Australians aged 8 to 15 used social media, the government said.

($1 = 1.5097 Australian dollars)

(Reporting by Byron Kaye, Claire Beers, writing by Alexandra Hudson; Editing by Andrew Heavens)

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