Almost 20,000 children and young people have been in contact with mental health services in Hampshire, Southampton and the Isle of Wight over the last year, new figures show.
Children's mental health charity YoungMinds said the figures are "harrowing", especially as students receive grades for A-level and GCSE exams.
The charity said increasing pressure at school and the impact of lockdowns during the coronavirus pandemic has affected young people's mental health, leading to a huge number of children needing support across England.
NHS Digital figures show 18,845 children and young people had at least one contact with mental health services in the NHS Hampshire, Southampton and Isle of Wight CCG area in the 12 months to May.
This was up from 18,380 in April and the most since local figures were first recorded in July 2021.
Across England, the number of children who had at least one contact with mental health services in the last year rose by 21% from 570,000 in the year to March 2021 – when national records began – to 690,000 in the year to May.
YoungMinds said the figures paint a "shocking picture" of the mental health of young people in the country.
It put the rise in children accessing mental health care down to a number of factors, including the pandemic and school pressures.
Olly Parker, head of external affairs, said: "The pandemic has certainly deepened the crisis in young people’s mental health, with huge disruption to students’ education, many of whom were also dealing with multiple pressures like difficult home environments, bereavement and other trauma."
Mr Parker also said schools do not have the resources to support the wellbeing of their students, who have felt particularly worried about exams since returning to school following the pandemic.
The Department for Health and Social Care said supporting children's mental health is a "major priority" and that it invested £79 million in 2021-22 to expand services to support more than 22,000 children and young people.
A spokesperson added it is expanding mental health support teams to cover 3 million pupils by 2024 and is increasing investment in services by at least £2.3 billion per year by 2024.
Meanwhile, the figures also show the number of children and young people across England who were still in touch with mental health services by the end of May topped 400,000 for the first time.
Of them, around 11,595 were in Hampshire, Southampton and the Isle of Wight – up from 11,075 in the same month last year.
The number of children still waiting for contact with mental health services nationally also reached a new high in May, when there were 460,000 open referrals.
In Hampshire, Southampton and the Isle of Wight, some 12,360 children were waiting to be seen at the end of May after being referred by a GP or other health professional.
Mr Parker said: "The reality is that month after month we are seeing devastating new records of young people struggling to get treatment and support for their mental health, and month after month, we are left waiting for the Government to take action and end this intensifying crisis."
He said the Government must urgently equip the NHS to deal with rising mental health pressures and deliver a mental health plan that has a "real focus on young people".