Almost 150 patients have gone missing from mental health hospitals at the Lancashire Care NHS Foundation Trust in the past two years.
Mental health charity SANE said it was increasingly concerned at the number of patients absconding from facilities, and blamed years of "relentless cuts" for creating appalling conditions on wards.
NHS figures show that 140 patients who had been sectioned under the Mental Health Act went AWOL – absent without leave – from Lancashire Care NHS Foundation Trust between April 2017 and March 2019.
A patient is defined as AWOL if they leave the facility they are detained in without permission, or fail to return after being allowed out on temporary leave.
Marjorie Wallace, chief executive of SANE, said absences among sectioned patients could lead to an increased risk of suicide.
She said: “We are increasingly concerned at the number of patients across the country that go missing for one reason or another, particularly those who become acutely ill without their medication and who can become a risk to themselves and others.
"We need urgent action to prevent patients going absent, or we risk an increase in suicides amongst this group.”
Across England, the number of incidents increased by 4.4 per cent over the two years, from 3,316 in 2017-18 to 3,462 in 2018-19.
Of the patients who went missing over the two-year period, 130, or 93 per cent , returned voluntarily.
Across England, 11 patients died whilst AWOL over the two-year period.
Alison Cobb, specialist policy advisor at the charity Mind, said it was difficult to draw definitive conclusions from the figures.
However, she said that the Mental Health Act is used in a way that fails to treat people with dignity and respect.
"Hospital wards can be stark and inhospitable, and when people are sectioned they are sometimes subject to unnecessary restrictions and practices such as physical restraint, seclusion or forced medication," she said.
"When someone is in hospital with a mental health problem, they are very unwell and need to be in a safe, therapeutic environment until they have recovered sufficiently to be discharged.
"Mental health services have a responsibility to ensure the safety of those in their care and any failings, including people absconding, should be thoroughly investigated."
An NHS spokesman said an extra £2.3bn was being invested in mental health services as part of the NHS Long Term Plan.
The money will go towards making sure inpatient facilities are properly resourced as well as early interventions for patients to prevent problems escalating.
He added: "The Government is rightly reviewing the Mental Health Act to protect some of the most vulnerable people in our society."