The number of mental health patients in England who had to travel away from their local area to get care has risen by almost a quarter over the past year, figures seen by the BBC suggest.
Some patients have been sent hundreds of miles for treatment because no beds are available locally, the data shows.
The online journal Community Care sent Freedom of Information requests to all 56 English mental health trusts.
NHS England said it was determined to improve mental health services.
The Royal College of Psychiatrists said delayed discharge and poor social care were exacerbating the problem.
Data from 37 trusts that responded showed there were 4,447 patients sent out of their area for treatment in 2014-15 - up 23.1% from 2013-14, when 3,611 patients were sent out of their area.
There was also an increase in the cost of caring for these patients - from £51.4m in 2013-14 to £65.1m in 2014-15, figures from 29 trusts showed.
According to the data, the longest journeys carried out by patients were trips from Bristol to Livingston (370 miles), Cumbria to London (270 miles), and Southampton to Harrogate (260 miles).
'I didn't know where I was'
Daniel Gillan, 40, from Margate, Kent, has suffered from mental health problems since he was 18.
In the middle of a crisis in late 2013, he was sent to a hospital in Weston-Super-Mare in Somerset - 226 miles away.
When he had to be admitted last month, there were no local beds available again.
This time, he spent most of June in Manchester - 281 miles away.
"The problem is my admissions have got further and further away from Margate as time goes by," said Daniel.
"If the beds are full here, the next closest bed that becomes available is the bed you're going to get. The closest bed in my case was Manchester."
The distance meant that neither family nor friends were able to visit him.
"I didn't know where I was, I didn't have a clue. I knew I was a long, long way from home as it had taken so long to get there but I didn't know where in the country I was."
While some mental health trusts, such as Oxleas and South London & Maudsley, have managed to reduce their use of out-of-area beds, most have increasingly had to transport patients to other parts of the country.
The trusts with the biggest increases in patients treated out of area from 2013-14 to 2014-15 were:
- Avon and Wiltshire: 162 to 446
- Camden and Islington: 154 to 338
- Norfolk and Suffolk: 112 to 270
- Southern Health: 171 to 372
Paul Farmer, chief executive of Mind, said the figures showed a "very clear message" that mental health services were struggling to deliver care.
He said: "It is unacceptable that so many people are being driven hundreds of miles away from their loved ones in search of a hospital bed, at a time when they are often scared, vulnerable and most in need of the support of family and friends and familiar surroundings."
Previous research by BBC News and Community Care found that more than 2,100 psychiatric beds have been closed in England since 2011.
The problems have led to the Royal College of Psychiatry launching an inquiry into acute care.
Its interim report, published on Wednesday, does not blame the bed closures for the difficulties patients are experiencing.
Instead, it says delayed discharges and poor community services are causing the problem.
"The biggest thing is to get some people in beds out of them," said Lord Crisp, who is chairing the inquiry.
"We need better ways of treating people in the community. [More] beds alone won't solve that - it's getting better housing, better alternatives to care, keeping people at home."
'Determined to improve'
Ministers have increased funding for mental health services and urged local commissioning groups to properly fund these services in a bid to ensure psychiatric patients are treated as well as physical patients in the NHS.
Dr Martin McShane, NHS England's director for people with long term conditions, said the Mental Health Taskforce had been set up to improve mental health services over the next five years.
He added: "We are determined to improve mental health services and address the distress and unwarranted costs associated with out-of-area placements which are unacceptable."