Digital youth service ReachOut said it has seen a 20 per cent surge in people accessing its online advice relating to LGBTIQ issues since August, when the postal survey became Turnbull government policy.

ReachOut – a frontline group that has about 1.5 million unique visitors to its website every year – said its online forums have also recorded a sharp increase in activity, with young gay people reporting feeling scared and tired of personal attacks.

One of the country's top mental health experts – former Australian of the Year, Professor Patrick McGorry – is in no doubt the spike is linked to the divisive debate unleashed by the postal survey campaign.

"We are hearing a lot from LGBTIQ people that this is reviving traumatic experiences, particularly from their school years," said Professor McGorry, now the executive director of Orygen, the National Centre of Excellence in Youth Mental Health.

"Australia is on the threshold of something really positive but we do have to manage the risk to vulnerable people over the course of the debate."

While ReachOut and Orygen have gone public with their concerns about the spike in demand, Fairfax Media understands half-a-dozen of the nation's most prominent mental health organisations have been part of crisis talks during the last three weeks. Some have taken their concerns directly to the government.

ReachOut CEO Jono Nicholas said young LGBTIQ Australians were discriminated against every day and were already at high risk of self-harm.

The national debate about their right to marry was "heightening this level of distress".

"The debate around the postal survey has been, and will continue to be, a significant drain on both the LGBTIQ community and the mental health organisations that support them," he told Fairfax Media.

"We fear Australia will be counting the cost of the postal survey for many years to come, and not just to the budget."

Another major service under pressure from the increased demand, but which did not want to be named, said young gay people were reporting feeling "hated by Australians" as a result of the debate. 

The groups say they are hearing not just from gay people but from friends and family similarly distressed about the debate. They say they fear most of all for young people who don't seek help, with concerns thousands of young people are suffering in silence and at risk of harm as the 'no' campaign intensifies.

Opponents of same-sex marriage officially launched their 'no' campaign in Sydney on Saturday, led by conservative politicians Cory Bernardi, Matt Canavan and Concetta Fierravanti-Wells. Supporters of the reform launched the 'yes' campaign in capital cities across the nation on Sunday.

Many same-sex marriage advocates wanted a free vote on the issue in federal Parliament and opposed a public vote – whether by plebiscite or postal survey – partly because of fears about the mental health impacts.

But some opponents of the reform have dismissed the mental health concerns of the campaign, including Senator Canavan, a Nationals MP who said people should stop being "delicate little flowers".

"Can't we just all grow a spine and grow up? The debate hasn't been that bad," Senator Canavan said in response to warnings from the National Mental Health Commission last week. The worst of the debate had actually come from "vile tweets and statements we've heard from 'yes' campaigners", he said.

Federal Liberal Party vice-president Karina Okotel said last week it was not just gay and lesbian Australians facing harassment. She said she had been the victim of "vitriolic abuse" for her stance against same-sex marriage.

"A culture has developed whereby it's acceptable to vilify, mock, abuse and shame anyone who stands in the way or even raise questions about whether we should legalise same-sex marriage. I have been called a homophobe, a bigot and been told that my views are disgusting," she told the National Press Club this week.

National Mental Health Commission co-chair Allan Fels said the survey debate had heightened discrimination against gay and lesbian Australians, with LGBTIQ people experiencing "damaging behaviour in their workplaces, communities and in social and traditional media".