The number of NHS child and adolescent psychiatrists has fallen by 6.3% over the past four years, their professional body has warned.
The Royal College of Psychiatrists said the workforce must be increased if the Government is to commit to a four-week waiting time target, as recently set out in its Children and Young People's Mental Health Green Paper.
It warned that in Kent, Surrey and Sussex there are just 3.75 child and adolescent psychiatrists per 100,000 children.
It is calling on the Government to add NHS child and adolescent psychiatrists to its official shortage occupation list as it said recruiting from overseas is crucial to achieve the proposed four-week waiting time against rising demand.
The college said applicants for jobs not on the shortage list may be rejected for a visa even if they are desperately needed by the service trying to employ them.
It found the number of NHS child and adolescent psychiatrists at all grades declined by 6.3% between November 2013 and November 2017. For consultants alone the fall was 6.9%.
Dr Bernadka Dubicka, chairwoman of the Royal College of Psychiatrists' Child and Adolescent Faculty, said: "Earlier this year an Indian child and adolescent psychiatrist had their visa application rejected because the quota for Tier 2 visas had been reached and they did not qualify as a priority on the shortage specialty list.
"Short staffing in child and adolescent mental health services is no secret. We are already struggling, and the Government's own green paper impact assessment predicts a rise in referrals.
"We are now calling for the child and adolescent psychiatrists to be added to the shortage occupation list.
"Recruiting from overseas is key to quickly employing more qualified doctors specialising in children's mental health and will ensure the profession is seen as a priority by the Home Office."