The NHS is struggling to fill shifts around the clock as it deals with a new generation of workers who want flexible working, it has been claimed.
Young people joining the health service have high expectations of their employer and want more say over when they work, a trust chief executive said.
The shift in the workforce is placing pressure on the health service and creating a generational clash with long-standing NHS staff, he said.
Latest figures show the number of staff vacancies across the NHS increased in the first quarter of the year, and is expected to rise further by the end of the year.
The chief executive, who spoke on the condition of anonymity, said: "What we are seeing is massive intergenerational issues with our workforce as it changes.
"The younger generation now joining the NHS, they have got massive expectations about what the offer is from us as employers, to be the employer of choice for them, and it's just a hard act to meet, I think.
"There's no sign that people are joining the NHS for long careers, and that the offer that we've got around pensions and security and those sort of things are enough these days.
"People are wanting huge amounts more in terms of flexibility, variety, options, and they think much more in terms of short-term careers, five-year horizons rather than 20-year horizons."
Meeting these expectations is "quite a big ask" for NHS Trusts, he said, which need to make 24/7 rotas work and try to get people to work as part of a team.
He added: "When you've got people who want to work with a lot of flexibility around part-time, they want to work when they want to work, it doesn't really make it easy between people who are prepared to make that sacrifice - as long as others are - to work the difficult shifts, the unsocial hours, the nights, the weekends on a regular pattern."
The chief executive of a separate NHS trust said the shortage of staff means it is difficult to make people work unsocial hours.
"We don't have the luxury of saying it's 24/7 or you haven't got a job, because they'll go somewhere else," he said.
"So I think that the overall deficit of the workforce is probably a greater challenge than the flexibility that the workforce offer."
There were 107,743 vacancies in England at the end of June, up from 98,475 in March and bucking a downward trend in 2017/18, according to the latest NHS Improvement quarterly report.
Think tank The King's Fund warned nursing shortages "risk becoming a national emergency".
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