Almost 6000 young people aged 12 to 24 presented to emergency departments for mental health problems in Hunter New England in 2022/23.
The figure amounted to a rise of 33 per cent in a decade.
The soaring rate of mental health among this age group has been attributed to social media addiction, climate change concerns and financial pressure.
Now it's being linked to hot weather.
UNSW Sydney research found links between hot weather and an "increase in suicidal thoughts and behaviours" among those aged 12 to 24.
It showed that the number of young people in NSW presenting to hospitals for these reasons increased with the temperature.
Researchers studied more than 55,000 emergency department presentations of youngsters at risk of suicide from November to March from 2012 to 2019.
The statewide study, which included Newcastle and the Hunter, found these presentations increased by 1.3 per cent for every 1 degree rise in daily mean temperature.
Lead author Cybele Dey, a psychiatrist and conjoint lecturer at UNSW Sydney, said there was a "clear link" between mental distress and hot weather.
"Negative social media posts rise, along with emergency presentations and calls to Lifeline," Dr Dey said.
Dr Dey said the hotter western areas of Newcastle and the Hunter made it more challenging for people to cope with higher temperatures.
Socio-economic disadvantage was also a factor.
Those without air conditioning and limited access to green space and waterways faced further troubles in staying cool, literally and psychologically.
"Big established trees are the equivalent of a good air-conditioning unit in terms of how much it cools the surrounding area in hot weather," Dr Dey said.
Sea breezes and the quality of housing were also considered to be important factors in determining how people cope with heat.
Dr Iain Perkes, a psychiatrist and senior lecturer with UNSW's School of Clinical Medicine, said the findings were "quite staggering".
"While we haven't established causality here, the type of pattern would point to a cause-and-effect response," Dr Perkes said.
Dr Dey said the "hotter it is, the worse it gets" with the emergency presentations for suicidal thoughts and behaviours.
This suggested there may be "a biological mechanism at play when young people get too hot".
"There was an increase in presentations on the first moderate hot day," she said.
This suggested there was "more likely to be a biological effect, rather than a flow-on effect from factors like poor sleep".
"The heat itself looks to be doing something to increase people's distress and that is supported by other literature."
She said previous research showed an "increase in negative sentiment on social media and decrease in positive posts on hotter days".
"The hotter it is, the more toxic social media gets.
"So even if you're sitting in a comfy airconditioned place, you will still experience distress on social media from people in places that are too hot."
Doctors for the Environment Australia spokesperson James Scott said "hot weather is increasing, with global heat records being broken almost every month".
Professor Scott, a study co-author, reaffirmed that "climate pollution is contributing to increased extreme weather, including heat".
"We need governments to take research like this into account before approving any new fossil fuel projects," said Professor Scott, a child and youth psychiatrist.
Dr Dey highlighted that the study was "not about concern about climate change affecting the mental health of young people".
"Climate distress is important, but this is about hot weather itself affecting young people," she said.
She said public health messages about heat should include the risks to mental health.
