One in 10 positions were not filled at Southern Health at the end of 2022, new figures show.
The figures come as a staff body for nurses says NHS nurses are being put under "intolerable pressure" as there "simply aren't enough of them".
New figures from NHS England show 9.9% of full-time equivalent positions at Southern Health NHS Foundation Trust were unfilled as of the end of December.
At the end of March 2022, this figure was 10.8%.
Vacancies do not mean these jobs are not being carried out, as a shortfall in permanent employees may be covered by temporary or agency staff.
Of 212 trusts across England, 79 (37%) had a vacancy rate of 10% or more – with Bradford District Care Trust having the highest, at 23.3%.
The NHS cautions discrepancies between trusts may be due to "transient labour populations" and operating models "designed to utilise different proportions of temporary workforce".
General secretary of the Royal College of Nursing, Pat Cullen, said: "Recruiting and retaining nursing staff in the NHS has become a serious challenge on the back of over a decade of pay cuts."
She said a lack of staff was impacting the quality of care they can provide to patients.
"Until we begin to turn the tide and fill these vacant posts, the NHS will not be able to tackle the backlog in care. This is why we are urging the Health Secretary to get back round the table and negotiate with us," she added.
The vacancy rate for nurses has risen from 9.9% in March 2020, before the pandemic, to 10.8% at the end of last year.
Across NHS trusts in the South East, 5,994 (10.9%) nursing positions and 1,075 (5.1%) doctors' roles were unfilled at the end of December 2022.
For all NHS trust staff in the region, 8.9% of positions were unfilled – up from 8.8% a year before.
Caroline Waterfield, director of development and employment at NHS Employers – part of the NHS confederation – said: "We know that the NHS is not immune to the challenges facing the rest of the UK economy in terms of a very competitive labour market.
"Not only has it been very tricky to attract the right number of suitable candidates into some roles, we’ve also seen higher levels of turnover as colleagues move jobs within the health and social care sector and into other industries."
"In some clinical roles, such as nursing and doctors, recruiting from overseas has supplemented UK training and enabled vacancies to be filled," she added.
Ms Waterfield urged Government to implement the "overdue" long-term workforce plan for the NHS immediately.
A Department of Health and Social Care spokesperson said: "There are record numbers of staff working in the NHS, with over 51,500 more people compared to a year ago – including over 5,300 more doctors and over 12,300 more nurses.
"We want to build on this progress and will publish a workforce plan shortly to ensure that we have the right numbers of staff, with the right skills to transform and deliver high quality services fit for the future," they added.