Some 160,000 staff were quizzed
Nearly half of NHS staff feel so overstretched they fear they cannot do their jobs properly, a survey shows.
The Healthcare Commission poll of 160,000 workers across England also showed many did not feel valued.
Unions said the figures were worrying as under-staffing was one of the key problems highlighted in the critical report on Stafford Hospital last week.
But ministers said more people than ever were being employed by the NHS and the problems reported were improving.
The poll, which is carried out each year by the regulator, covers the full range of NHS staff from doctors and nurses to support staff.
Some 47% of staff said they did not feel there were enough people to do the job, down from 51% in 2007.
A third said they did not feel valued by bosses and just over a quarter had experienced work-related stress - however both of these had fallen slightly in the previous year.
The poll also revealed that half of ambulance staff had said the vehicles were not kept in a good state of repair.
Anna Walker, chief executive of the commission, said progress was being made but more work was needed.
"There are real lessons to be learned from this survey about leadership, management and team work."
Karen Jennings, head of health at Unison, said the findings were worrying, pointing out that inadequate staffing levels were at the heart of the critical report into Stafford Hospital's emergency care where death rates were significantly above average.
"NHS employers need to listen to staff and must act when they are told they do not have enough time or people to do their jobs properly and deliver quality patient care."
But the survey has been published as the latest workforce census showed that NHS staffing levels have hit a record high.
There are now nearly 1.4m staff employed in England - a rise of over 25 percent in the past decade.
Health minister Ann Keen said it was clear working in the health service was a "rewarding career" as many more nurses, matrons, consultants and GPs were now being employed.
She said staff across the NHS were helping "deliver high quality patient care to all".
But the Tories accused the government of creating too much bureaucracy as the figures also showed that the rise in managers was outstripping that of many clinical staff.
Shadow health secretary Andrew Lansley said: "These spiralling management costs show that Labour's repeated pledges to spend NHS money on the things that matter most were just empty rhetoric."