Health bosses fear the Covid-19 crisis could see the number of people waiting for NHS treatment double to 10 million by the end of the year.
The NHS Confederation said challenges include a backlog of cases, maintaining social distancing, and staffing.
The body, which represents health and care leaders, said emergency funding and longer-term spending were needed.
The Department of Health has said it will continue to provide the resources, funding and support the NHS needs.
Guidance had been issued on how the NHS “should start to restore services in a safe way”, a spokesman added.
It comes as Prime Minister Boris Johnson is to announce further plans to ease lockdown restrictions in England later, with zoos and drive-in cinemas among the businesses expected to be allowed to