A major incident has been declared at Colchester hospital after a surprise inspection this week found patients being inappropriately restrained and sedated without consent and “do not resuscitate” notices being disregarded.

The ward concerned has been closed to new admissions, an emergency control centre has been put in place to address capacity problems, and patients are being urged to go to A&E only if they have a serious or life-threatening condition.

Inspectors from the Care Quality Commission (CQC) found that the Essex hospital is struggling with “unprecedented demand”, but the Guardian understands concerns were also raised about safeguarding issues relating to inappropriate restraint, resuscitation and sedation of elderly people, some with dementia.

The news comes as the health secretary, Jeremy Hunt, warned of “real pressure” on A&E departments this winter and announced a £300m fund to help. He said on Friday: “We are very aware that over this winter there is going to be some real pressure there. The pressures are higher than they have ever been before in the system.”

Colchester hospital said it was facing unprecedented demand. Routine elective operations were being rescheduled and a drive was under way to discharge as many patients as possible where it was safe to do so. Extra staff are being drafted in.

Initially, the hospital said the CQC concerns related to the large number of patients entering the hospital through A&E. But health chiefs have now admitted to the Guardian that safeguarding concerns were also highlighted during the inspection.

The inspectors questioned whether informed consent had been given by some patients in the hospital’s emergency assessment unit for some medical procedures, the Guardian understands. The unit closed down admissions in the wake of the inspection.

Dr Lucy Moore, chief executive of Colchester Hospital University NHS foundation trust, said: “The CQC raised a small number of safeguarding concerns when its team gave immediate feedback at the end of the inspection on Wednesday.”

A spokesman repeatedly refused to confirm or deny the specific allegations relating to the use of restraint and sedation and regarding “do not resuscitate” notices.

The major internal incident was announced on Friday during the public part of a regular hospital board meeting. The findings from the CQC visit were discussed in the private part of the meeting.

Moore said: “A high number of escalation beds [emergency overflow beds] are in use and we are, unfortunately, having to postpone some elective operations. Clearly, this is a difficult time for the trust.”

This is the latest crisis to hit the hospital, which was put in special measures by the health regulator Monitor last November after data inaccuracies in cancer treatment targets meant it breached its licence to provide health services. The CQC found staff were being bullied to alter figures. A police investigation was launched into the data issues.

Peter Wilson, acting chairman of the hospital trust, said: “The CQC visited here and visited A&E and emergency admission unit departments. Disappointingly, although they commented favourably on some aspects, their general view was that the situation had not improved. We have already put actions in place to address some of the issues they face.

“We are, however, facing an unprecedented demand at the front end and have declared today a major incident, which means a whole-hospital review of demand, capacity, staffing levels and discharge processes and other opportunities for improvement.We have established a control centre under the command of the chief operating officer.”

A trust spokesman said: “The trust continues to function fully and effectively, and the people of north-east Essex can be assured that we are here for them and they can help by using our emergency department [A&E] only if they have a serious or life-threatening condition. We anticipate that the internal major incident will not be called off for another week or so.”

Katherine Murphy, the chief executive of the Patients Association, said the alleged ill-treatment of patients was “horrific” and reminiscent of the Mid Staffordshire scandal. She said: “I’m saddened, horrified and distressed to hear of such allegations. If they are confirmed, they are horrific.

“It’s deeply alarming that despite Mid Staffordshire, Winterbourne View and all the reports that have been published, that this inhumane treatment and lack of care and compassion continues to happen today, especially with such vulnerable elderly people.”

Prof Mike Richards, the CQC’s chief inspector, said: “CQC carried out an unannounced inspection at Colchester hospital this week in response to concerns. The inspection looked at the accident and emergency department and the emergency assessment unit (EAU).

“Following the inspection, we gave feedback to the trust about our safeguarding concerns so that it could take appropriate action to ensure the safety and wellbeing of its patients. We will return to carry out further inspections at the trust and we are working urgently with Monitor to resolve these issues.

“A full report of CQC’s findings will be published on our website in due course.”

North East Essex clinical commissioning group, the local GP-led NHS body that sends patients to the hospital and pays for their treatment, said it was concerned by what it knew of the CQC’s findings. “We are very disappointed to hear that the CQC has seen little improvement to A&E services since their last visit earlier this year [and] of particular concern is the issue of safeguarding patients.

“While we await their full report, we are working with the hospital trust and other partners to address the CQC’s urgent concerns highlighted during their visit this week. This includes supporting safe discharges and preventing avoidable admissions.”

Outside the hospital’s A&E, a noticeboard said the department was experiencing “high patient volumes”.

It added that the current wait for a doctor was three hours, and more than an hour for a nurse. “Please use the walk-in centre or contact your GP where possible,” it said.

Staff and patents leaving the hospital appeared surprised at the news that an incident had been declared.

A local resident who had been visiting his wife in maternity care said: “I’ve found that there have been no problems with the service we’ve had – so far, anyway. I’ve seen the reports about things but I’m not sure what the situation there is.”

A member of staff who was, like others, reluctant to comment, nodded when asked about overcrowding and said: “It’s just an overflow situation.”

The CQC’s most recent inspection report on Colchester hospital, published in July, found that it required improvement in the key areas of safety and responsiveness and had inadequate leadership. It was found to be good in terms of how effective and caring it was.

The CQC said that those findings would normally lead to enforcement action but because the hospital was already in special measures it had instead informed Monitor of the breaches.

A government spokesman said: “We established the role of the independent chief inspector of hospitals, and set up the toughest inspection regime in the world, precisely to root out poor care wherever it takes place – meaning that any problems can be confronted and sorted out quickly, unlike at Mid Staffs where sadly they were allowed to persist for years.”