Fewer children and young people at Hampshire and Isle of Wight Healthcare Trust are waiting to access mental health treatment, new figures show.
Ahead of last year's general election, Labour had said waiting lists for those referred for mental health support were "too high, and shamefully so for young people".
In its election manifesto, it pledged to "bring waiting times down and intervene earlier".
But mental health charities have warned of persisting "agonising waiting times" for children and young people to access treatment and called for comprehensive reforms and investment.
NHS England figures show around 40,260 people sought access to Hampshire and Isle of Wight Healthcare NHS Foundation Trust's mental health services at the end of May, including about 17,020 aged 18 and under.
Around 9,165 children and young people were still waiting for a first care contact at the end of May, with an average waiting time of 351 days since their referral was issued.
In comparison, about 9,940 were waiting for a first contact a year earlier at the end of May 2024, and the average waiting time was then 410 days.
Some values are rounded to the nearest five, while figures below five are suppressed to protect patients' identities.
Across England, some 1.87 million people were in contact with mental health services at the end of May – up 8% from 1.74 million a year earlier, and the second highest figure since records began in 2016.
This included 617,197 children and young people aged 18 and under, which was up 9% on the previous year.
Of those, 377,017 were still waiting for a first contact at the end of May. And for them, the median waiting time was 276 days – up significantly from 200 a year earlier.
YoungMinds interim chief executive Abigail Ampofo warned these statistics "lay bare the shocking scale of the mental health emergency facing young people".
She said: "For years, these figures have been jumping to new record highs and successive Governments have failed to act with the urgency and with the level of change that is needed.
"Today they reveal agonising waiting times for most young people who desperately need support.
"We know this will often make their mental health worse, putting extra strain on the system. The knock-on effects on the individual, the NHS and the economy are incalculable."
She said "it is clear" the Government acknowledges "real and lasting action is needed", but warned "this has not yet been matched with solutions that meet the scale and urgency of the challenge".
Dania Hanif, chief executive of the Association of Mental Health Providers, warned: "Our members are deeply concerned that, despite repeated government promises to reduce mental health waiting times, the situation for many young people is getting worse.
"These delays have devastating consequences for young people's education, wellbeing, and family life, often pushing them to crisis point."
She called on the Government to "prioritise investment in prevention and early intervention".
Alexa Knight, director of England at the Mental Health Foundation, said these statistics "are a clear indication that we cannot treat our way out of the UK’s mental health crisis".
She welcomed the Government's decision to make prevention a priority in its 10 Year Plan for Health, but warned "their ambition on this needs to be greater if they want to support people to stay mentally well".
"We need to see a coherent approach across all parts of Government – not just the NHS – through a comprehensive plan for mental health," she added.
An NHS spokesperson said: "The NHS is seeing record demand for mental health support, with a 64% increase in young people accessing our services compared to pre-pandemic, but we know there is much more to do.
"We have significantly boosted the children and young people’s mental health workforce and the 10 Year Health Plan for the NHS will expand mental support teams in schools and colleges to all pupils and learners by 2029-30 to offer early help."
The Department of Health and Social Care was contacted for comment.