Hundreds of patients have had hospital appointments cancelled while others are being resuscitated in corridors as hospitals shut down in the extreme heat. Doctors have set out the 'unacceptable' impact the heatwave is having on the NHS, with vital equipment, including MRI scanners, failing as temperatures rise. The hot weather has also prompted a surge in the number of A&E visits as elderly patients struggle to stay cool, prompting several trusts to declare critical incidents. The Norfolk and Norwich University Hospitals NHS foundation trust, raised the alarm after its MRI scanners stopped working as a direct result of the extreme heat. The trust said at least 362 outpatients appointments had been cancelled and it was prioritising inpatients and those on suspected cancer two-week wait pathways. Magnetic resonance imaging - or MRI - scanners are used to help doctors see what is happening inside the body, and are often used to diagnose brain tumors and injuries. Without them, hospitals risk becoming 'settings where extreme heat puts patients at risk, rather than places of safety,' Dr Hillary Williams, clinical vice president of the Royal College of Physicians, warned. 'Patients are facing overcrowding, and there are issues with machines, laboratories and kidney dialysis - all fundamental to providing safe patient care. NHS hospitals risk becoming places where extreme heat puts patients and staff at risk if buildings are not upgraded, the clinical vice-president of the Royal College of Physicians warned Speaking to The Guardian, she continued: 'The impact of heatwaves cannot be overstated. There is a sense of foreboding when we see the weather forecast, because we know what is to come, and there is very little staff can do.' Other hospitals have reported similar problems during the heatwave. In Portsmouth, the Queen Alexandra hospital declared a critical incident after its cooling units failed, resulting in 'elevated temperatures' across the hospital. This has led to 'significant disruptions across several of [the trust's] services', including operating theatres, diagnostic scanning facilities and cardiac laboratories.Meanwhile, NHS Hampshire and Isle of Wight said soaring temperatures have put the entire health system in the region under immense pressure. It said the critical alert issued by the UK Health Security Agency this week indicates a risk to life, including among people who are normally healthy, prompting the trust to trigger measures to maintain services. The Royal Devon and Exeter Hospital followed suit, declaring a critical incident on Thursday evening 'due to the widespread nature of impacts the extreme heat and humidity' were having on both staff and patients. The London ambulance service also reported its highest number of life-threatening emergencies in a single day in its history.