Thousands of young people undergoing a mental health crisis, including those who are potentially suicidal, are having to wait more than four hours for A&E care, NHS figures show.

Almost a fifth of the under-18s who seek A&E help in England for psychiatric problems such as depression and self-harm are not seen within the supposed maximum of four hours.

Figures released by hospital trusts to Labour under freedom of information laws showed that while 82.2% of such patients are seen within four hours, 17.8% are not. Across the 65 acute trusts that supplied data, 11,210 of the 13,567 under-18s with a mental health problem were seen within four hours but 2,357 waited longer.

In all, 26,593 children and young people aged 17 or under attended A&E last year as a result of mental health issues. If the 17.8% of them who had to wait beyond four hours at the 65 trusts was replicated across that entire cohort, that would mean as many as 4,733 waited that long.

The disclosure prompted warnings that troubled young people might harm themselves while waiting for delayed care and calls for under-18s suffering a deterioration in their mental health to be able to access help quicker so they did not have to turn to an A&E.

“Young people should have the support they need for their mental health to prevent them from reaching crisis point and no child should be faced with long waits for help in a crisis”, said Barbara Keeley, Labour’s shadow minister for mental health and social care, who obtained the figures.

Emma Thomas, the chief executive of the charity YoungMinds, warned that long waits could make things worse for a young person in crisis.

“We work with young people who have waited months for mental health support and who have started to self-harm or become suicidal, who then go to A&E because they don’t know where else to turn.

“But despite the best efforts of staff, it’s often a stressful and frightening environment, and not somewhere a desperate child or teenager should have to wait for hours before getting help.”

Thomas added that the “worrying figures” showed that, despite progress by the NHS in extending patients’ access to mental health crisis care, more services in schools and community settings were needed.

“If young people do reach crisis point, there need to be places they can go instead of A&E, where they can get the help they need in a space that feels safe”, she said.

NHS England has pledged in its Long Term Plan to ensure that everyone in England – children, young people and adults – can access mental health crisis services around the clock by 2023-24 by calling the 111 telephone helpline.

It plans to create “24/7 provision for children and young people that combines crisis assessment, brief response and intensive home treatment functions” and set up crisis resolution home treatment services for adults.

It also plans “a range of complementary and alternative crisis services to A&E and admission within all local mental health crisis pathways”.

The Conservatives did not respond directly to Labour’s findings. A spokesperson said: “One of the great changes of our age is to treat mental health on a par with our physical health. Demand for mental health services is rising and the stigma of the past being taken away.

“As a result, the NHS is treating twice as many people with mental health conditions than in 2010 and is delivering the biggest expansion of mental health services in a generation – backed by an additional £2.3bn in real terms by 2023-24.”

• This article was amended on 5 December 2019 because an earlier version gave an incorrect figure of 13,205 as the total for under-18s who seek A&E help in England for psychiatric problems in the relevant released information. The correct figure was 13,567.