Health officials are worried many people are not seeking treatment because they fear contracting Covid-19, thereby jeopardising their survival and potentially becoming collateral damage to the virus.
Recent research found four in 10 people are too worried about being a burden on the NHS to seek help from their GP.
NHS chief executive Sir Simon Stevens stressed the NHS is still there for non-Covid patients who might be suffering from a stroke, heart attack, and other killer conditions.
It is predicted there will be one million fewer visits to A&E this April compared to 2.1 million visits recorded over the same period last year.
Senior clinicians from the Royal College of Paediatrics and Child Health and medical health charities such as the British Heart Foundation and Stroke Association are also worried.
The new public health campaign will be rolled out from next week reminding people to contact their GP or call 111 if they need urgent care, and attend a hospital if they are told to do so.
Those in an emergency must still call 999.
It also calls upon Britons to use other vital services such as cancer screening and treatment, maternity appointments and mental health support as normal.
Sir Simon said: "While NHS staff have pulled out all the stops to deal with coronavirus, they have also worked hard to ensure that patients who don't have Covid-19 can safely access essential services.
"Ignoring problems can have serious consequences - now or in the future."
Due to efforts to ramp up capacity in the face of the coronavirus threat, the NHS now has 33,000 urgent care beds at its disposal in traditional hospitals.
The NHS has also overseen the construction of seven new Nightingale field hospitals around the country.
The campaign will include information from doctors, nurses and patient groups to highlight how the health service has adapted to the pandemic to ensure safe access to all types of urgent care.
Professor Carrie MacEwen, chair of the Academy of Medical Royal Colleges, said: "We are very concerned that patients may not be accessing the NHS for care because they either don't want to be a burden or because they are fearful about catching the virus.
"Everyone should know that the NHS is still open for business and it is vitally important that if people have serious conditions or concerns they seek help."
The British Heart Foundation has reported a 50% fall in the number of people attending A&E with heart attacks, thereby risking their survival.
Earlier this week, Cancer Research UK warned 2,250 new cases of the disease could be going undetected each week - partly down to patients' reluctance to go and see their GP.
Health Secretary Matt Hancock has also voiced his concern.
Speaking in the House of Commons on Wednesday, he said: "If you are told to go to hospital, the place you need to be is in hospital.
"The NHS is there for you and can provide the very best care if you need it."