Patients may only be admitted to A&E with a referral or if they arrive by ambulance, under new proposals submitted to ministers.
The Royal College of Emergency Medicine says that in order to reduce transmission of coronavirus, patients may have to get approval from their GP or NHS 111 before receiving emergency care.
Under plans submitted by the college to Matt Hancock, the rule could be broken in “life or death” cases.
The experts warn that more people will die from Covid-19 if A&E departments return to the overcrowding that was widespread before the pandemic.
In a second part of its plan, "hot clinics" will be set up for patients who are referred with less time-critical complaints, such as severe headaches requiring a scan.
"Non-emergency" patients would be separated from the emergency department.
The third measure would increase the number of clinicians taking NHS 111 calls.
The calls have been shown to increase appropriate and timely referrals as well as reduce unnecessary ambulance call-outs.
Dr Katherine Henderson, president of the Royal College of Emergency Medicine, said: "Going back to how we used to operate is not an option - patients will die if we do.
"It was just four months ago when we were seeing overcrowding on a record scale in emergency departments. It was unacceptable then and put lives at risk.
"To go back to that now will lead to avoidable patient and staff illness or death.
"If departments are crowded, we cannot protect patients and staff. Crowding has long been associated with avoidable mortality, and Covid-19 reinforces and multiplies this risk.
"We must have a way to enforce social distancing in emergency departments to ensure that patients do not become infected while seeking healthcare.
"If supermarkets can get this right, then the very institution that people entrust with their health must do so too.”
Data released since the peak of the pandemic shows A&E attendance has dropped to its lowest levels since records began since the start of the Covid-19 crisis.
This is believed to be because patients are fearful of catching the virus if they attend hospital, but also because they mistakenly believe they will not be seen.
Dr Adrian Boyle, vicepresident of the Royal College of Emergency Medicine, said: "It is unconscionable that we return to the overcrowded departments that we have had in the past where people are waiting next to each other and in corridors and not socially distancing.
"This is now unacceptable. We need to have maximum occupancy and some of the less time-critical patients will need to be looked after away from the emergency department in hot clinics.