The Act leader has suggested smartphones could be banned for under-16-year-olds.

In a speech to a business leaders' dinner on Wednesday night, David Seymour said it's clear anxiety, depression and self-harm has increased in children and young people since the advent of smartphones.

He has suggested Parliament could prohibit the purchase, possession and supply of smartphones to under-16s, instead only allowing teenagers to use 'dumb-phones', which don't have access to social media apps.

"We already prohibit adults from supplying minors with tobacco and alcohol, for example.

"The object is tangible, the rule is understandable, and reasonable adults support the purpose of the law. A smartphone is just as tangible."

Citing political commentator Ani O'Brien, Seymour said that instead of regulating the platforms, the device should be targeted instead.

"Put simply, why don't we deal with the hardware instead of the software?"

The government is already considering a social media ban in line with Australia's and the United Kingdom's - but the Act Party has said it doesn't support it.

Seymour said a ban on social media is too hard to implement, and won't work.