NSW's public mental health services are short between $550 and $600 million annually, according to more than 700 pages of internal documents released under a parliamentary order.
A further $187 million per year was also necessary for the community-managed mental health sector, the private briefing from December 2024 stated.
"Releasing the full quantum of the gap could require NSW to deliver one of the largest expansions of mental health services (and infrastructure) in recent history," the departmental analysis said.
But the papers also showed NSW Health warned Health Minister Rose Jackson it could be problematic for the government should the figures be released publicly.
The confidential briefing said the shortfall could "potentially create reputational damage if the government cannot produce funding to address the stated gap".
''The Minns Labor government was clearly told how poorly mental health care is funded in NSW,'' Greens MP Amanda Cohn, who first called for the document to be produced, said.
"Instead of fixing the problem, they tried to bury it.
"People who need mental health care are waiting for days, not hours, in emergency departments, or are putting off their next appointment because they can't afford it."
Quizzed on the funding shortfall, Premier Chris Minns said it was likely more than $600 million.
"It's a complicated picture when it comes to health services, particularly mental health services, (but) we've increased the budget for mental health services by 20 per cent," he said.
"I'm going to be really blunt with everybody, there's only so much money we can invest in it ... I'm not prepared to raise taxes."
Royal Australian and New Zealand College of Psychiatrists NSW chair Ian Korbel said the trove confirmed the daily experiences of professionals working in a broken system and patients suffering.
"The documents released quantify in greater detail what patients, families and clinicians experience every day, with our mental health system under immense pressure," he said on Wednesday.
Mass resignations by psychiatrists in 2025 and an industrial umpire ruling forced the government to provide a 20 per cent pay bump for 12 months in a bid to attract and retain staff.
The sector has also been hampered by fatal mishaps, including the case of Queensland man Joel Cauchi, who was diagnosed with recurrent schizophrenia and fatally stabbed six people at Westfield Bondi Junction in 2024 before being shot dead.
In February 2026, two patients who escaped from Cumberland Hospital, Australia's largest mental health facility, allegedly caused the deaths of three people in separate crimes days from each other.
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