More than a dozen people with suspected autism in Bury waited too long for a diagnosis in December, new figures show.
Autism is a lifelong condition which impacts how people communicate and interact with the world.
The National Autistic Society said a diagnosis is vital, and called on the Government to provide imminent funding to clear the soaring backlog of people with suspected autism across England.
Sunday is the United Nations-sanctioned World Autism Awareness Day, which this year focuses on a "neuro-inclusive world for all".
But the latest NHS Digital figures show approximately 15 people suspected of having autism were waiting for an assessment after being referred by a specialist in the former NHS Bury CCG area at the end of December.
NICE guidance says no patient should wait longer than 13 weeks, but every person in Bury had already breached this standard at the end of last year.
In December 2021, around five people had an open referral – of which five had been waiting for more than 13 weeks.
The figures are rounded to the nearest five, while clinical commissioning groups were abolished and replaced with integrated care boards across England.
Meanwhile, in December 2019, before the coronavirus pandemic, 10 people were waiting for an autism diagnosis.
Nationally, more than 140,000 people were estimated to be waiting for a diagnosis at the end of last year – up from 47,000 in December 2019. Of these, more than 120,000 (87%) have waited more than 13 weeks.
The National Autistic Society said a diagnosis is "vital to getting the right help and support" and that many struggle at school, work or home, or can develop mental health problems like anxiety or depression without one.
Tim Nicholls, head of influencing and research, said: "Without significant, long-term funding for diagnosis services across the country, many autistic people will continue to face traumatic long waits for an assessment.
"As a result, many will be left struggling without the right support at school, work and home. The Government must urgently invest in diagnosis services, as set out in the national autism strategy for England, and make sure that autistic children, young people, adults and their families get the support they need.
Of the people waiting for a referral, around five were aged 17 and under.
The Department for Health Social care said it is "committed to reducing delays and improving access to support".
A spokesperson added: "We are investing £2.5 million this year to ensure patients are seen more quickly, on top of £74 million in the first year of our national autism strategy, and NHS England is producing national guidance to improve outcomes for autistic people throughout their diagnosis."