Reddit has launched a challenge in Australia's highest court against the nation's landmark social media ban for children.

The online forum is among 10 social media platforms that must bar Australians aged under 16 from having accounts under a new law that began on Wednesday.

The ban, which is being watched closely around the world, was justified by campaigners and the government as necessary to protect children from harmful content and algorithms.

Reddit is complying with the ban, but in its case, will argue that the policy has serious implications for privacy and political rights. It is the second such legal challenge, with two Australian teens also awaiting a hearing in the High Court.

"Despite the best intentions, this law is missing the mark," Reddit said in an update on its website.

"There are more effective ways for the Australian government to accomplish our shared goal of protecting youth."

Australia's Communications Minister Anika Wells has previously said legal threats will not sway the government.

"We will not be intimidated by big tech. On behalf of Australian parents, we will stand firm," she told parliament after news of the first legal challenge broke last month.

In that case, which the High Court has agreed to consider at an as-yet-undecided date next year, two 15-year-olds from New South Wales are claiming that the social media ban is unconstitutional because it infringes "the implied freedom of communication on governmental and political matters".

"Democracy doesn't start at 16 as this law says it will," Macey Newland told the BBC after their case was filed.

The ban, which has excited global leaders and worried tech companies, has also been criticised by some who argue blanket prohibition is neither practical nor wise.

Experts fear kids are going to circumvent the ban with relative ease - either by tricking the technology that's performing the age checks, or by finding other, potentially less safe, places on the net to gather.

And backed by some mental health advocates, many children have argued it robs young people of connection - particularly those from LGBTQ+, neurodivergent or rural communities - and will leave them less equipped to tackle the realities of life on the web.

But the policy is wildly popular with parents and has won the support of people like Oprah, and Prince Harry and Meghan, the Duchess of Sussex.

In a statement on their website, the pair lauded the "bold" action from Australia but said "it shouldn't have come to this".

"We hope this ban is only the start of a reckoning between society and the tech companies that built these platforms with growth as their first principle instead of safety."

Various governments, from the US state of Florida to the European Union, have been experimenting with limiting children's use of social media. But, along with a higher age limit of 16, Australia is the first jurisdiction to deny an exemption for parental approval in a policy like this - making its laws the world's strictest.

Reddit said the law forces "intrusive and potentially insecure verification processes on adults as well as minors", isolates teens engaging in "age-appropriate community experiences" and creates an "illogical patchwork of which platforms are included and which aren't".

"There are more targeted, privacy-preserving measures to protect young people online without resorting to blanket bans."

The case is not "an attempt to avoid compliance" or "an effort to retain young users for business reasons", it added.

"Unlike other platforms included under this law, the vast majority of Redditors are adults, we don't market or target advertising to children under 18," it said.

The other platforms affected by the ban include Facebook, Instagram, Snapchat and TikTok.