Four people have been arrested after carers at a residential hospital were secretly filmed abusing adults with learning difficulties, police said.
Avon and Somerset Police launched an investigation after a BBC Panorama reporter filmed images of apparent misconduct at Winterbourne View, in Bristol.
All four have been released on police bail. The hospital's owners, Castlebeck, have apologised and suspended 13 employees.
The recordings, made in February and March this year, appear to show carers punching and slapping patients, throwing cold water on them, and pinning them to the ground with chairs.
Other footage showed residents being dragged into showers while fully clothed and being taunted by the carers.
Care Services Minister Paul Burstow said government regulator, the Care Quality Commission (CQC), had been asked to conduct an urgent investigation.
Avon and Somerset police confirmed that three men - aged 42, 30 and 25 - and a 24-year-old woman were arrested as part of their ongoing investigation into the hospital.
Clinical psychologist Andrew McDonnell told the BBC he was shocked by the footage and described some of the examples captured on film as "torture".
He told the programme that basic techniques for dealing with patients with challenging behaviour were ignored.
After viewing one excerpt, he said: "This is not a jail... people are not here to be punished.
"This is a therapeutic environment. Where's the therapy in any of this? I would argue this is torture."
In a statement, the Care Quality Commission said, following an internal review, it recognised that "there were indications of problems at this hospital which should have led to us taking action sooner.
"We apologise to those who have been let down by our failure to act more swiftly to address the appalling treatment that people at this hospital were subjected to," it said.
Care Services Minister Paul Burstow said people deserve to receive "safe and effective care" from every care provider.
He also said he had "confirmed with CQC that they should undertake a series of unannounced inspections of services for people with learning disabilities."
Lee Reed, the chief executive officer of the home's operators Castlebeck, said: "I was shocked, disgusted and ashamed by what I saw on Panorama.
"Having spent my entire career in health and social care, I intend to leave no stone unturned to ensure that this type of horrific event is never allowed to happen again."
The company said it is now in "active consultation" with the appropriate authorities with regard to the future of the hospital, which cares for up to 24 patients, employs around 50 members of staff and is funded by taxpayers.
Castlebeck has launched an internal investigation into their whistle-blower procedures and are reviewing the records of all 580 patients in 56 facilities.
The vulnerable patients filmed by Panorama have been moved to safety.
The hospital charges taxpayers an average of £3,500 per patient per week and Castlebeck has an annual turnover of £90m.
Panorama's Undercover Care: The Abuse Exposed was broadcast on BBC One on Tuesday 31 May at 2100 BST and is available to view in the UK on the BBC iPlayer.