Rat droppings were found behind cupboards at the unit
A rat infestation has left patients at a Huddersfield mental health unit "scared", a nurse has told the BBC.
NHS bosses at St Luke's Hospital in Crosland Moor said they took the problem "very seriously" and had hired a pest control company to tackle it.
One of the nurses, who did not want to be named, said rat droppings were found in the dining area and the garden had become a no-go area.
"I work there and I have seen patients be really, really scared," she said.
The unit accommodates about 40 people, most with acute mental illness. Some elderly people with general medical problems also use the site.
The scale of the infestation was revealed just before Christmas when plumbers were working in the dining room area of the Beaumont Wing.
"When the plumbers were working they pulled out the cupboards and there were loads of rat droppings and it smelled really strong," the nurse said.
"Patients are concerned about eating in the dining room."
Alan Davis, a director at South West Yorkshire Mental Health Trust, said: "We have been aware that there has been a problem with rats before Christmas and we have been working with the Calderdale and Huddersfield Trust, who are the owners of the site, to actually deal with it.
"A new specialist pest control company was appointed by the trust just before Christmas.
"They have developed a full action plan which included increasing the bait and monitoring the site.
"I would want to reassure people that it has not been ignored. Plans are well in place and we are dealing with this matter."
Figures obtained by the Conservatives under the Freedom of Information Act last August showed that Calderdale and Huddersfield NHS Trust was one of the 89 trusts in England which had more than 50 visits from pest controllers between January 2006 and April 2008.
Professor Robert Smith, a pest control expert and the Dean of Huddersfield University, said: "If you see signs of droppings it means the rats are about and they are probably getting a lot further than you realise.
"Apart from the droppings they are also dribbling urine all over the place and there is a very serious disease called Weil's Disease that you can get in rat urine.
"So, to me, rats inside buildings are never acceptable - that is much too close for comfort.
"You particularly don't want rats around in a hospital because they will alarm patients and visitors, they will spread disease and they may cause structural damage."