By Alex Mitchell in Sydney

Two influential Labor premiers back a possible ban on social media up to the age of 16, saying a big stick could be needed to force tech giants to curb mental harms caused by their products.

A long line of experts queued up to support the proposed youth ban, at a two-day summit jointly hosted summit by the NSW and South Australian governments that kicked off in Sydney on Thursday.

Meta and other social media companies were represented at the event, which heard little from opponents of the ban or any of the school-aged children it would affect.

There was compelling evidence the most vulnerable age for social media users was between 14 and 16, said NSW Premier Chris Minns, pointing to a possible policy that only allowed for use at that age with parental consent.

“We don’t want to be in a situation where we go through a summit, legislative change, widespread momentum in the community … and end up with the wrong policy,” he said.

“So I think (the age limit) should be as high as we can make it.”

The platforms would ultimately need to implement any age-limiting measures but if they did not, laws should be in place to hold them accountable, Mr Minns added.

“We’ve got a bank of evidence here about social media companies’ response to regulation reform … I don’t think I’m jumping to a false conclusion when I say they’re unlikely to comply,” he said.

Increases in loneliness, depression and self-harm among young people could be directly linked to social media’s rise as its use can lead to less sleep, more social comparison and less in-person interaction, psychology professor Jean Twenge said.

But establishing age restrictions was too simple an approach and more would be needed to achieve positive outcomes for today’s youth, some experts said.

“Mental health is a complex phenomenon … technology is not capable of causing these things on their own,” Young and Resilient Research Centre professor Amanda Third said.

“What we need is the political will to hold different sectors of the online safety ecosystem to account, to deliver on their responsibilities to children and young people … I don’t know why we’re having these silly debates about banning things, we’ve just got to get in there and fix it.”

Research psychologist Rachel Kowert agreed and said a ban, rather than trying to tackle online behaviour and mental health among children, lacked balance.

“These spaces are not all good or all bad, but the evidence really points to more good than bad,” she said.

Prime Minister Anthony Albanese and a host of state leaders back youth bans but are yet to reveal where the cut-off will be set.

Federal legislation is due to be introduced before the end of 2024.

SA Premier Peter Malinauskas, who first floated a state age-based ban in May, also put forward a minimum age of 14 with parental consent until 16.

But he said compelling evidence at the summit could point to a higher limit.

“There needs to be a degree of urgency applied from governments and their leaders around the nation … we can genuinely be a world leader when it comes to the regulation of social media,” he said.

A letter signed by more than 120 mental health and other organisations, experts and academics has been sent to the prime minister and the NSW and SA premiers.

One of those signatories, the youth-focused ReachOut, said social media was routinely used by children for mental health support, often because access to professional treatment was limited.

“Young people are using social media to access free mental health information available around the clock … it’s vital to discuss what other mental health supports will be provided if social media bans are introduced,” chief executive Gary Groves told AAP.

The summit shifts to Adelaide on Friday.