More than 10,000 children in Surrey Heartlands were in contact with mental health services in the year to September, new figures show.
It comes as more children than ever accessed mental health services across England, with the number of open referrals having almost doubled throughout the coronavirus pandemic.
Mental health charity YoungMinds said the Government is failing to take action against a "deepening" crisis.
NHS Digital figures show around 13,420 children in the former NHS Surrey Heartlands CCG area were in contact with mental health services in the year to September.
Nationally, 710,000 children accessed mental health support – the highest observed figure since comparable records began in March 2021.
Meanwhile, the number of children with an open referral has rocketed during the pandemic.
Some 465,000 children waiting for a mental health appointment following a referral at the end of September – up from 250,000 at the end of September 2019.
In Surrey Heartlands, 11,660 children had an open referral at the end of September.
Laura Bunt, chief executive at YoungMinds, said: "Instead of action, young people get broken promises in the form of scrapped plans and missed opportunities.
"We need the Government to turn the tide on this emergency – it must commit to reducing prevalence and tackle the reasons why so many young people are struggling with their mental health."
"We need an ambitious plan that matches the scale of need focusing on prevention, investment and improving services," Ms Bunt added.
Further NHS Digital figures show children in England aged between 11 and 16 with a probable mental disorder were five times more likely to have been bullied in person – and four times more likely to be bullied online – than those unlikely to have a mental disorder in 2023.
Meanwhile, more than one in four children with a probable mental disorder had a parent who could not afford activities outside school.
This is compared to just over one in 10 of those unlikely to have a mental disorder.
NHS mental health director Claire Murdoch said: "NHS staff are working harder than ever to meet the increased demand and we have fast-tracked mental health support for millions of pupils in schools and colleges, as well as significantly expanding the children’s mental health workforce."
The Department for Health and Social Care said it will invest an additional £2.3 billion a year in mental health services, meaning an additional 345,000 children and young people can access support.
A spokesperson added mental health support teams are being rolled out in schools and colleges, while the Government is focusing on growing the mental health workforce – in March, there were 143,000 full-time equivalent NHS staff working in mental health services, up from 136,000 in September 2022.