Experts from the Royal College of Psychiatrists have warned the problem facing the country will get worse before it gets better with new analysis revealing almost 400,000 children and 2.2 million adults sought help for mental health problems during the crisis.
While the effect of lockdown and coronavirus has affected people of all ages, children appear to be particularly susceptible.
Some 80,226 more children and young people were referred to specialist mental health services between April and December last year, up by 28 per cent on the same months in 2019 to 372,438.
Meanwhile, 600,628 more treatment sessions were given to children and young people, up by a fifth on 2019 to 3.58 million.
Overall, 18,269 children and young people needed urgent or emergency crisis care, including assessments to see if they needed to be sectioned under mental health laws.
This is an increase of 18 per cent on the figures for 2019 and includes assessment for illnesses such as anorexia and other eating disorders.
The Royal College said overall almost 400,000 children and 2.2 million adults sought help for mental health problems during the pandemic, with 1.68 million more mental health sessions delivered over the past year compared with the year before.
Dr Bernadka Dubicka, chairwoman of the child and adolescent faculty at the Royal College of Psychiatrists, said: "Our children and young people are bearing the brunt of the mental health crisis caused by the pandemic and are at risk of lifelong mental illness.
"As a frontline psychiatrist I've seen the devastating effect that school closures, disrupted friendships and the uncertainty caused by the pandemic have had on the mental health of our children and young people.
"Services were already struggling to cope with the number of children needing help before the pandemic hit, and they risk being overrun unless the Government ensures the promised money reaches the front line quickly."
Dr Adrian James, president of the Royal College said: "The extent of the mental health crisis is terrifying, but it will likely get a lot worse before it gets better.
"Services are at a very real risk of being overrun by the sheer volume of people needing help with their mental illness.
"While the recent funding announcement is welcome, we need this money to reach mental health services as soon as possible to tackle this crisis."
The data also show that adults are suffering, with more than one million additional treatment sessions given to adults between April and December last year, an increase of 8 per cent on 2019.
Some 159,347 urgent or emergency crisis referrals were made for adults - an all-time high - and an increase of 2 per cent on 2019.
The government has given an additional £500 million to help launch a mental health recovery including specialist support for children.
Health minister Nadine Dorries said: "I am acutely aware of how difficult this pandemic has been for many, especially children and young people, and I remain absolutely committed to supporting the mental wellbeing of everyone.
"Early intervention and treatment is vital, and we are providing an extra £2.3 billion a year to mental health services, this will help an additional 345,000 children and young people access NHS-funded services or school and college-based support by 2023-24.
"Last month we announced a cross-government mental health recovery action plan, backed by an additional £500 million, specifically targeting those that have been most impacted by the pandemic including those with severe mental illness, young people, and frontline staff.”
Join our commenting forum
Join thought-provoking conversations, follow other Independent readers and see their replies