Health chiefs have warned the NHS needs an emergency cash boost of between £200 million and £350 million to cope with the added demands of winter.
They warn the NHS could face its worst winter in recent history.
NHS Providers, the trade association that represents hospital, mental health, community and ambulance service trusts in England, called for the emergency cash injection to enable the NHS to manage patient safety risk in the winter months.
The organisation said failure to make the investment will lead to longer waiting times and will put the safety of patients at risk as local trusts struggle to meet the expected demands.
A report found the level of planning and support for this winter is better developed than last year, and emergency care performance has been given greater priority.
It also said extra social care funding is helping to increase capacity in about a third of local areas, but these improvements are being outweighed by a combination of increasing risks.
It added that demand for emergency care continues to rise while staff shortages are growing, and primary and social care capacity, as a whole, remains "very challenged".
NHS Providers also said trusts are under greater financial pressure than last year and therefore less able to afford the extra capacity they urgently need.
Chris Hopson, chief executive of NHS Providers, said that last year the NHS came under pressure like never before, adding: "At its height, the NHS had to provide 4,500 additional beds a day - equivalent to more than eight extra hospitals. Patient safety was compromised as local services struggled to cope with the pressures."
Shadow health secretary Jonathan Ashworth MP said: "Reports of 'dangerous' bed shortages this winter putting patient safety at risk are extremely worrying and will lead to yet more patients being left in the back of ambulances or stranded on hospital trolleys for hours on end.
"At the general election, Labour promised a cash injection to cope with this year's winter crisis.
"The Government urgently needs to follow our lead and to heed the advice from health bosses to provide an immediate funding boost this winter to avoid serious harm to patients."