Almost 25,000 NHS jobs have been axed in the last three years, the Royal College of Nursing (RCN) said.
Since April 2010, 24,836 health workers have lost their jobs, including 4,800 nurses and 4,000 healthcare assistants, a new report for the RCN found.
And a further 44,000 posts in the UK which are earmarked to go before April 2015, according to the RCN's Frontline First report. The union said that cuts to the nursing workforce are still taking place.
"Our latest Frontline First report paints a very worrying picture for the future of the health service, and the Government cannot afford to ignore these warning signs," said RCN chief executive and general secretary Dr Peter Carter.
"Tens of thousands of posts have already been cut with even more expected.
"The effects are already being felt on the ground, with hospitals and emergency departments unable to cope with soaring demand."
An RCN spokesman said that there could be a "massive nursing shortfall" in the future because of nursing student places being cut and an ageing workforce.
The report says that between 2010-2011 and 2012-2013 the number of nursing training places across the UK has reduced from 24,904 to 21,529.
Dr Carter added: "If the Government does not change course, the effects of these cuts are likely to be magnified as the number of newly qualified nurses continues to fall, and the health care needs of an ageing population continue to increase demand on the NHS.
"We need to see an immediate end to the short-term, slash and burn cuts to nursing staff levels and the failure to plan for the long term, which are damaging patient care and bringing the health service to its knees."