More than a dozen children received urgent treatment for eating disorders at the Solent Trust last year, new figures show.
Anti-eating disorder charity Beat said the Government and NHS England must "develop a fully-funded mental health recovery plan" after the number of children waiting for help soared nationally during the coronavirus pandemic.
NHS England figures show 19 children were urgently treated for eating disorders at Solent NHS Trust in the year to June – down from 47 over the same period two years earlier.
NICE guidance states that 95% of urgent referrals should be treated within one week.
But at the trust, just 14 cases (73.7%) met this threshold.
In the 12 months to June 2020, 42 of the 47 urgent referrals (89.4%) were seen within one week.
Across the country, the proportion of children with an urgent referral seen within one week fell from 88% in the year to June 2020, to 68% last year.
Across the same period, the number of children waiting for urgent treatment across England has increased fourfold – from 56 to 230.
Tom Quinn, director of external affairs at Beat, said the rise in waiting times and lists is "very concerning", with many children experiencing heightened anxiety during the pandemic, and some reaching out for help with eating disorders for the first time.
"NHS eating disorder treatment has increased dramatically since before the coronavirus, and NHS services are not getting the funding or staffing that they need," said Mr Quinn.
Mr Quinn called on the Government to publish a fully-funded mental health recovery plan – including announcing added funding and a workforce strategy – to ensure every person with an eating disorder can access treatment quickly.
The number of children waiting for eating disorder treatment following routine referrals in England has also rocketed during the pandemic – 1,500 children were waiting for treatment at the end of June, more than triple the 441 two years before.
NICE Guidance says 95% of routine cases should be treated within four weeks of a referral, but just 69% were seen within this timeframe in the year to June.
At the Solent Trust, 132 of 137 children (96.4%) with routine referrals were seen within four weeks.
The Department for Health and Social Care said it is "determined" to provide mental health care to those with eating disorders and that it will invest in services to treat an additional 345,000 children and young people by 2024.
NHS England said the pandemic has had an impact on the nation's mental health but that an additional £2.3 billion will be invested in services to aid treatment.