The NHS in England is in a "dangerous downward spiral" by "haemorrhaging" nurses, experts have warned.
The Royal College of Nursing (RCN) urged ministers to act after new analysis concluded more than 10% of the nursing workforce left NHS employment in each of the past three years.
BBC analysis of workforce figures from NHS Digital found that more than 33,000 walked away last year - with the number of leavers surpassing the number of those joining the workforce by 3,000.
The RCN said that patients were "bearing the brunt" of strain put on NHS nurses.
Janet Davies, chief executive and general secretary of the RCN, said: "These are disappointing, but not surprising, figures. The Government must lift the NHS out of this dangerous and downward spiral.
"In England, we are haemorrhaging nurses at precisely the time when demand for health and care services has never been higher.
"Most patient care is given by NHS nurses and, each time the strain ratchets up again, they are the ones who bear the brunt of it.
"We already know there are 40,000 unfilled nurse jobs and things continue to head in the wrong direction. There cannot be safe care for patients while the Government continues to allow nursing on the cheap."
She later told BBC Radio 4's Today: "What we are finding is that nurses are telling us that they find it impossible to do their job in the way that they wish to.
"They love being a nurse, they are really dedicated and when they cannot do that they feel no alternative but to leave. They don't want to be providing poor care."
It was time to legislate for "safe staffing levels", she said, and measures were needed to attract people into the profession.
Professor Jane Cummings, England's chief nursing officer based at NHS England, told the BBC: "We do lose people that need to be encouraged. We're in the process of bringing in lots of nurse ambassadors that are going to be able to talk about what a great role it is, to be able to tell their story, so we can really encourage people to enter the profession and for those in the profession, to stay in it."
She said the NHS was trying to make nursing more attractive, adding: "We are beginning to see some fantastic good practice giving people flexible, rewarding careers. The key is getting it everywhere."
Meanwhile the Government is increasing the number of nurse training places by 5,000 this year - a rise of 25%.
A Department of Health and Social Care spokesman said: "Nurses are at the heart of our NHS and that's why there are 11,700 more on our wards since May 2010.
"We want to keep these hardworking staff in our NHS and also build a workforce fit for the future - that's why we announced the biggest ever expansion of nurse training places with 5,000 more available from 2018, opened up extra routes into the profession and continue to support nurses to improve work-life balance and work more flexibly."