Nearly 5,500 mental health patients in England had to travel out of their area last year because of a lack of hospital beds, new figures show.
Some patients had to travel nearly 300 miles, while one trust had to declare a major incident.
The figures, obtained through Freedom of Information requests, are 13% higher than last year.
Care minister Alistair Burt said the problem was unacceptable and promised to stop it within five years.
Being sent "out of area" for treatment means a patient being cared for in a unit not run by the trust whose care they are under.
It can occasionally be appropriate to send a patient outside their area if they need highly-specialised care, but experts say that routinely sending people away can increase the risk of suicide - and there have been repeated calls for the practice to be stopped.
But these figures, obtained by BBC News and Community Care magazine, show the problem is getting worse.
In 2014-15, 4,804 patients were treated out of area; in 2015-16 that figure had risen to 5,411 - a rise of 12.6% (according to data from 42 of 56 trusts).
Data from 28 trusts going back to 2011 shows the ever-worsening scale of the problem. In 2011-12 those trusts placed 1,215 patients out of area - in 2015-16 that had risen to 4,093, a rise of 236%.
'More scared, more alone'
Jessica Wilson has suffered from mental health problems for several years, including post-traumatic stress disorder and borderline personality disorder.
Last December, the 21-year-old, from Louth, in Lincolnshire, became ill and needed a hospital bed. None was available locally and she was sent to Roehampton in London - 170 miles from home.
"When I found out they were looking in Nottingham, I cried," says Jessica. "So when I found out I was going to Roehampton, it was a nightmare.
"It made me feel more scared, more vulnerable, more alone and totally confused."
Jessica spent three weeks in London. While she praises the care she received there, the distance meant neither her mother nor her local mental health team could visit.
"It was really hard for me," she says. "As part of my recovery, I feel my family need to be involved.
"So not seeing them, not being able to talk to them like I normally would, really affected me. I think if I'd been closer to home, my recovery would have been a lot stronger and a lot [quicker]."
The distances some patients had to travel include:
- Devon to Bradford - 286 miles
- Manchester to Southampton - 232 miles
- Leeds to Glasgow - 224 miles
Sue Scarborough's son was 15 when he was sent away from his home in Hull for treatment in Northumberland. She had to travel five hours to visit him, and describes the situation as having been "terrible".
"He just thought that I'd left him and I wasn't going to see him any more. He'd never heard of Northumberland and didn't know why he was there and what he was being treated for, which was appalling really.
"I could only visit on a weekend because of the distance, I don't drive. It was just disgusting."
Lib Dem MP Norman Lamb told the BBC's Victoria Derbyshire programme that sending people long distances for treatment was an "intolerable practice" and one he wanted to see banned.
"If you're in that setting, separated from your family, it actually prevents you from recovering properly.
"This would never happen with a stroke patient, or one with a heart problem. It's a discrimination, at the heart of our NHS, against people with mental ill health."
Mind chief executive Paul Farmer said that, despite repeated commitments from government and the NHS to improve the care of people in crisis, the rise in numbers of travelling patients was "truly a sorry state of affairs".
She added: "It costs more to do things badly, and the human cost is far greater. People with mental health problems deserve better.
"A mental-health crisis is an emergency just like a physical health emergency, and no-one should be expected to put up with a second rate service for either."
NHS England has repeatedly said it is committed to improving mental-health services, but the use of out-of-area beds has worsened every year since it was created.
It has been told by ministers to aim to eradicate the problem within five years.
'We had to draw attention to a crisis'
In January, Lancashire Care NHS Trust had to declare a major incident because of a lack of beds. It had to place 94 patients in out-of-area beds, while another 26 were waiting to be admitted.
"It's an unprecedented decision for a mental health trust to declare a major incident," says Sue Moore, chief operating officer at the trust.
"There is a lot of time spent focusing on the crisis in [accident and emergency].
"We had to really draw everyone's attention to the fact that there was a crisis here within mental health and it needed everyone to participate to mitigate that."
By declaring a major incident, Lancashire Care could suspend some planned activities and focus on the crisis, redeploying staff to help move people ready to be discharged and supporting those who had to be admitted.
The trust opened 22 beds - 10 in an assessment ward and 12 by partnering with a housing association that provided accommodation to patients still in hospital due to homelessness.
The effect has been dramatic, says Mrs Moore. There are currently just 20 patients in hospital beds out of Lancashire.
Mr Burt said it was "unacceptable that too many patients suffering from mental illness are receiving care so far from home".
"We have increased mental health funding to £11.7bn, have accepted the recommendation of the Mental Health Taskforce that the inappropriate use of out of area treatments for adults in acute care must be eliminated by 2020-21, and will work to a faster timetable if at all possible," he added.