A surge in child mental health cases is expected to emerge as schools reopen next week, amid warnings of a “crisis on top of a crisis” hitting vulnerable children during the pandemic.

Paediatricians, psychologists and charitable groups providing mental health support all told the Observer they were seeing increasing demand and warned of another surge as lockdown is lifted. Several reported longer waiting lists for young people in need of help.

Some charitable mental health services said they had seen a 70% rise in demand over the past three months, compared with the previous year. The number experiencing eating disorders, self-harm and even psychosis is causing serious concern. There are also warnings that the crisis is having a disproportionate impact on children living in poverty.

Karen Street, officer for mental health at the Royal College of Paediatrics and Child Health, told the Observer: “We are all really worried about what we’re already seeing, and really worried about what might be coming. We’re seeing an increased presentation to acute hospitals of children in crisis. What we found in the first lockdown is that things seem to go quite quiet on all fronts right at the beginning, but later there was a really steady and very big surge of young people presenting with eating disorders.

“That surge peaked in September and October, when they were back in school and the teachers had that opportunity to see them for the first time in months.

“What we’ve seen from members on eating disorders is that they’ve dropped slightly again in this lockdown. We’re all thinking, gosh, what’s going to happen now when they all go back to school? We’re all just feeling we’re going to see lots of slightly lost, sad, confused, anxious, disorientated kids coming back into school.”

Bernadka Dubicka, chair of the child and adolescent faculty at the Royal College of Psychiatrists, said the Covid pandemic had highlighted and intensified an existing problem in child mental health. “We’ve got a crisis on top of a crisis,” she said. “We had a pre-existing crisis in child and adolescent mental health before the pandemic. The indications are things just got much more difficult for many children and families, and also for the staff trying to provide services.

“We already have evidence of an increase in mental health problems among families living in poverty. We know the pandemic has hit many of those families the hardest. It’s extremely worrying.

“I think our prediction would be that [an increase in demand for services] is the direction things are likely to go in because of all the existing data that we have, and trends that we can already see. I’ve seen a lot of children that hit crisis on going back to school in September last year and are terrified about going back again.”

Julia Britton, director of charity Open Door, a community service for young people in north London, said in the last three months, she had seen “an increase of around 70-75%” compared to last year. “We’re aiming to see them for an initial assessment within four weeks, but they might then sit on a waiting list for anything from two to nine months, which we don’t want to see at all,” she said.

“We are seeing a big increase in suicidal thinking and self-harm, eating disorders, anxiety and of course, isolation.”

It follows a series of warnings that the funding for child mental health was failing to match the increased need even before the pandemic hit. Many local clinical commissioning groups are still spending less than 1% of their budget on providing children’s mental health services. Recent research suggests one in six children now has a mental health issue, while the 61,000 referrals to children and young people’s mental health services in England last November was a record high. It represented a 66% increase in the same month in 2019 and 139% higher than the same period in 2017.

A Department of Health and Social Care spokesperson said: “We know this year has been exceptionally difficult, especially for our children and young people, and hat for many it is having a real impact on their mental health.

“Early intervention and treatment is vital, and we are providing an extra £2.3bn to help an additional 345,000 children and young people access NHS-funded services or school and college-based support.

“We are also training a new dedicated mental health workforce to provide targeted support, and investing £8m to help upskill education staff so they can better respond to children’s emotional and mental health needs as a result of the pandemic.”