An official audit on one day in March this year revealed that nearly 500 people were detained under the Mental Health Act in Lancashire Care NHS Foundation Trust.
The Royal College of Psychiatrists said that while reasons for the rise were complex, one factor is that people are waiting too long to receive help for mental illnesses.
On March 31 this year, a snapshot was taken of people detained under the Mental Health Act in the Lancashire Care NHS Foundation Trust. On that date, around 485 were sectioned, though this was down from 520 at the same time in 2017.
The numbers provided by NHS Digital are approximate, to prevent identification of people sectioned.
The Mental Health Act is used in cases where people require urgent treatment and pose a risk to themselves or others. It can be imposed following an assessment by a mental health professional and a doctor.
Across England, more than 21,000 people were sectioned on 31 March, an increase of five per cent from a year previously – though part of this increase can be explained by some trusts not providing figures in 2017. Some trusts continued not to provide data for this year, meaning the true figure for 2018 is higher.
In total, the Act was used on 49,551 occasions across England in 2017-18, an increase of 2.4 per cent on the previous year. Some people will have been detained more than once.
Professor Wendy Burn, president of the Royal College of Psychiatrists, said: "More people being detained under the Mental Health Act represents more people with mental illness reaching crisis point. The reasons behind that are complex.
"What we do know is that people are waiting far too long to get help."
A poll conducted by the Royal College of Psychiatrists found that 24 per cent of people diagnosed with a mental health condition reported waiting more than three months to see an NHS mental health specialist, and six per cent waited more than a year.
Across England, the NHS Digital data showed that black and minority ethnic people are more likely to be sectioned. People from a black or black British background are more than three times as likely to be detained under the Act as white people.
An independent review of the Act, commissioned by the Government, is due to be published in December.
Professor Burn added: "We look forward to the recommendations from the Review of the Mental Health Act, which we hope will look beyond purely legislative changes to go some way to improving the care of people with mental illnesses, and addressing the reasons why BME people are disproportionately detained under the Act and placed on compulsory community treatment.
"Improving mental health services depends on the right number of well-trained staff, more medical students who choose psychiatry, and the right resources to meet the needs of patients, their families and carers."