More than 1,000 people in need of urgent mental health treatment were detained under the Mental Health Act in Hampshire, Southampton and the Isle of Wight last year, figures show.
The Law Society said planned reform of the Act must happen "sooner rather than later" after more than 50,000 people were detained in England in the year to March.
Figures provided by NHS Digital show at least 1,095 detentions were carried out across the former NHS Hampshire, Southampton and Isle of Wight CCG area in 2021-22.
That was a detention rate of 68 per 100,000 people over the year.
The NHS cautioned some figures are an undercount as a handful of organisations did not submit adequate data.
Around 53,340 new detentions under the Mental Health Act were recorded across England last year – an estimated 6% decrease compared to 2020-21. Of those, 34,840 saw the person restrained on being admitted to hospital.
Nick Emmerson, vice president of the Law Society of England and Wales, said: "These statistics show why reforming the Mental Health Act must be a priority for the Government.
“The current system means there is a risk that compulsory detention and treatment is used too often and that patients do not have enough involvement in decisions about their care.
“We welcome the Government’s commitment to reforming the Mental Health Act and support the introduction of new safeguards for patients refusing medication."
The Government's white paper on mental health reform, published in 2021, set out proposals to raise the threshold for detention and allow patients to have more autonomy over their treatment, as well as tackle disparities faced by people from black and minority ethnic backgrounds.
Last year, the national detention rate for black people stood at 342 per 100,000 population – more than four times as high as the rate for white people (72).
Paul Spencer, head of health, policy and campaigns at Mind, said he was "extremely concerned" by the figures.
"It is simply unacceptable that black people and those of us living in less well-off areas face greater rates of detention," he added.
"These figures paint a damning picture of the hurdles faced by marginalised groups in navigating the mental health system – which should be there to meet the needs of all of us – and illustrate how overdue reforms to the Mental Health Act and wider mental health system are."
A spokesperson for the Department for Health and Social Care said the decrease in detentions is a "testament to the positive steps" it has taken to support people with serious mental health issues.
They added: “However we recognise there is still work to do – we remain committed to ending the unequal treatment of people from black and other ethnic minority backgrounds with mental illness.
“Our draft Mental Health Bill is currently going through pre-legislative scrutiny with proposals to ensure anyone in a mental health crisis is treated with dignity and respect, and given greater control over their treatment."