Mental health groups are in urgent talks about how to deal with a dramatic spike in demand they are attributing to the same-sex marriage postal survey, with fears the situation will worsen further as the campaign goes on.

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.