Patients will be put at risk this winter unless the NHS in England is able to provide 10,000 more beds.
The British Medical Association's (BMA) warning is another sign of the Tory-manufactured crisis across the health service.
Dr Rob Harwood, BMA consultant committee chair, said "The NHS is facing an all-year crisis that is leaving patients in an intolerable situation.
"This winter could be the worst on record for frontline emergency care departments."
He added, "BMA analysis suggests hundreds of thousands of patients will be left waiting to see a doctor or stranded in cramped corridors on a hospital trolley waiting for a hospital bed to become available."
The BMA predicts that the number of accident and emergency (A&E) patients waiting for more than four hours until they are seen will increase to over a million between January and March 2019.
And, even after hospitals have decided to admit a patient, tens of thousands could be left lying on trolleys. The BMA analysis warns that "trolley waits" of four hours or longer could rise from 226,000 to over 300,000.
Chronic staffing and bed shortages mean hospitals won't have the capacity to deal with an anticipated rise in patient numbers and longer waits in A&E units.
Harwood said, "A key part of this problem is the lack of available beds within the NHS."
"Last winter saw incredibly high levels of bed occupancy, well above recommended limits."
The quality of patient care deteriorates as soon as bed occupancy rates rise above the recommended 85 percent—and deterioration accelerates once it goes over 92 percent.
Yet the occupancy rate peaked at over 95 percent last year—and could reach similar or worse levels this time around.
Harwood said, "At this level patients will struggle to get the attention and care they need."
The BMA said that the NHS will need up to 10,000 more beds to keep it under the minimum safe limit. While it can use 5,000 "escalation beds" opened last winter, it will also need 5,000 more general and acute beds.
It's no accident that the NHS is heading for one of its worst winter crises with a severe lack of beds.
Years of budget cuts and privatisation across the NHS and local government have undermined health and social services.
The number of hospital beds in England has fallen by 40,000 in the last 20 years to barely over 100,000.
There are only 2.7 beds per 1,000 people in Britain, which is the second lowest number in Europe.
The BMA's warning is another reason to kick out the Tories and their regimes of cuts and privatisation.