The NHS in England does not have enough beds or staff, health bosses say, ahead of the new financial year next week.
NHS Providers, which represents chief executives, warned the service was facing an impossible task in 2018-19.
The group said it meant hospital waiting lists would grow and long A&E waits continue.
But the government said it was taking steps to support the NHS, including pay rises for staff and the promise of a long-term funding settlement.
The pay rise - if agreed by the workforce by the summer - will be backdated to April and guarantees staff, excluding doctors, a minimum pay rise of 6.5% over three years.
Meanwhile, on Wednesday Prime Minister Theresa May committed the government to a long-term funding plan in the near future to end what she called annual "cash top-ups".
However, NHS Providers said neither of those would address the immediate pressures facing the health service.
It highlighted figures showing that one in 12 posts were vacant, including nearly 36,000 nurse jobs and 9,600 doctor posts.
The organisation also warned another 10,000 to 15,000 hospital beds were needed on top of the 100,000 already in the system.
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It said these problems meant:
- A&E units would fail to get back on track in terms of meeting the four-hour waiting time target - performance has dropped to is lowest level since the target was introduced in 2004
- waiting lists for planned operations would continue to grow and were likely to top four million people soon
NHS Providers also warned the finances of hospitals, ambulance trusts and community services were unravelling.
A deficit of more than £900m is being forecast - nearly twice as bad as originally forecast despite ministers announcing an extra £1.6bn for 2018-19 in last year's budget.
NHS Providers chief executive Chris Hopson said: "While we strongly welcome the prime minister's commitment to increase long-term funding for the NHS, it makes no immediate difference to the tough task facing trusts for next year."