The number of children being diagnosed with autism in Northern Ireland has more than doubled in five years.
Some health trusts have seen a three-fold increase and there are also 2,500 under-18s still waiting to be assessed.
Healthcare professionals and autism charities have pointed to increased awareness as a reason for the jump.
Kerry Boyd, the head of Autism NI, said her organisation is "inundated" with requests for support.
"The introduction of the Autism Act (NI) 2011 and the accompanying increase in awareness both within the general public and health and education professions may have contributed to a rise in the number of assessments carried out and resulting diagnoses," she said.
"Consequently Autism NI, which provides vital services, is inundated with requests for support and we are finding it increasingly difficult to fulfil this demand.
"As a result of this exponential increase, many families are not receiving an adequate level of support particularly in relation to early intervention."
Image copyright Getty Images
Image caption Children and adults may be missing out on educational support if there are delays
In total 2,345 children under 18 were diagnosed as autistic last year, compared with 1,047 five years previously.
The latest figures were obtained by the BBC after a freedom of information request to all five of Northern Ireland's health and social care trusts and cover the period between 2013-14 and 2017-18.
The figures do not distinguish between the different types of diagnosis, with the Northern Trust the only one to differentiate between Asperger's and autism.
The Belfast Trust saw the highest increase, from 171 cases in 2013-14 to 567 in 2017-18.
There was also a trebling of the numbers diagnosed in the Southern Trust, from 72 to 234 in the five-year period.
The South Eastern Trust had the smallest rise but diagnoses were still up 66% from 230 cases in 2013-14 to 378 last year.
In keeping with trends that show males are more likely to be diagnosed, almost three times more boys than girls were found to be autistic in the five years.
'Failed to deliver'
The Autism Act NI was passed by the Northern Ireland Assembly and was designed to ensure those affected are afforded the same entitlements as people with other disabilities.
It also bound all government departments to plan, cooperate and implement an agreed autism strategy.
However, in 2016, Autism NI and the National Autistic Society NI published the Broken Promises report, which said the legislation and resulting strategy and action plan had "failed to deliver on its promises of help for autistic people, their families and carers".
It said: "Their experiences suggest that life is getting more, rather than less, difficult for autistic people."
The document called on the Northern Ireland Assembly and the Stormont Executive to take action but within a year the institutions had collapsed.
Image copyright SPL
Image caption The number of diagnoses had "skyrocketed" in recent years, says Dr Alan Stout
More than 1,000 children in the Northern Trust are awaiting a diagnosis, while the Belfast and Western Trusts have 600 or more children waiting for an assessment.
Ms Boyd said: "Autism NI would advocate that more resources should be invested immediately in autism services in order to ensure the best possible outcomes for individuals with autism and their families."
Concerns raised by parents or schools often lead to a formal assessment, in which a multi-disciplinary team of healthcare professionals comprising the likes of a psychiatrist and speech and language therapists decide whether to recommend a diagnosis.
Dr Alan Stout, the chair of the Northern Ireland GP Committee of the British Medical Association, said figures have "skyrocketed" due to "increased awareness" and changes to the criteria under the 2011 legislation.
Image copyright Annie Davison
Image caption Annie Davison says she faced a long wait to get her two children diagnosed
"A number of years ago we were also placing other types of conditions, such as Asperger's, but now they are all categorised as being on the spectrum of autism and the threshold has also been reduced for what constitutes being on the spectrum," he said.
"We do tend to notice that the diagnoses are getting younger and younger - it has big, big implications if the diagnosis can be confirmed.
"It helps the understanding for the school and the parents.
"It can mean getting school assistants and enables the altering of various environmental and social factors in the school - for example we have seen an increasing number of pupils getting dogs."
Dr Stout said that increased resources and enabling more assessments outside of hospitals could help reduce the backlog.
"Being able to see the patients and diagnose them in a community setting is more valuable - sending them to hospital (can be) very intimidating (for those affected)."
The long process of getting a formal diagnosis is a huge struggle for many parents.
Annie Davison, from Sydenham in east Belfast, said it had been "very stressful" waiting for her son Terence and daughter Emma to be tested.
Both children have been diagnosed with Asperger's syndrome.
"I was noticing some things in my son, as I have other family members, such as my niece, who have been diagnosed," she said.
"[In Terence's case] I had a feeling something wasn't right, from the age of about two-and-a-half.
"Nursery said they had no concerns and so did the primary school when he arrived."
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Image caption A autism diagnosis can lead a child to avail of extra educational support such as a classroom assistant
After advice from a school nurse that she should take Terence to his GP, Mrs Davison was referred to the autism team.
"It was just over a year waiting for the diagnosis.
"It was very stressful, waiting, having to research autism myself - there was no input from anybody else.
"He was getting frustrated and wasn't able to communicate his needs.
"He was very hyper and was staying up all night - we were in limbo and having to manage it ourselves."
Schools need 'more resources'
Mrs Davison said that after her son's diagnosis she put in place a home routine and altered his "visual" environment".
While her children are now receiving extra educational support, she is still lobbying for greater resources.
"There are a lot of people who are not getting help in schools," she said.
"The NHS and schools are under tremendous pressure but there needs to be more training and resources.
"If a teacher is working with a child with autism there needs to be training for them."