SOUTHBRIDGE (CBS) — A nurse at Harrington Hospital was stabbed by a patient in the emergency room Wednesday morning.

Worcester County District Attorney Joseph Early Jr. said 24-year-old Conor O’Regan came to the hospital around 10:15 a.m. for general medical treatment and attacked the nurse with a knife before running off.

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Early said at a press conference Wednesday afternoon that investigators have no idea what, if anything, prompted the attack.

The nurse was treated and stabilized in the ER and then taken by Life Flight helicopter to UMass Medical Center in Worcester.

Conor O’Regan allegedly stabbed a nurse at a Southbridge hospital (Facebook Image)

“No one expected to come to work today and have to be working on one of their good, good friends in the emergency room,” Early said.

The nurse, a 40-year veteran nearing retirement, is in critical but stable condition. Her name has not yet been released.

The nurse’s neighbors in Dudley are stunned. “She’s very helpful, she does a lot of stuff around the neighborhood, I just couldn’t believe this happened,” the neighbor said. “You just got to watch out there’s crazy people everywhere.”

A nurse was stabbed by a patient in the ER at Harrington Hospital in Southbridge Wednesday. (WBZ-TV)

O’Regan was captured off campus and is currently being held at the Southbridge Police Department.

He is charged with aggravated assault and battery with a dangerous weapon (a knife) and assault with intent to murder.

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“Things escalated quickly,” Early said.

Early said authorities are working to find out more about O’Regan.

“I’d like to thank the emergency room personnel, specifically the nurses and doctors, for their quick response and the way that they reacted to help save the victim’s life–a job that was made even more difficult under the added stress of the fact that they were working on their friend,” Early said.

“As you can imagine, no one came to work today expecting any of this, next you know they are working on one of their best friends trying to save her life,” he said as he continued to praise “a group of great nurses and two trauma surgeons who are among the best.”

Harrington Hospital said patient admissions to the emergency room were currently being “restricted and managed by ER and public safety staff,” and that their other locations were operating normally.

“Our thoughts and prayers are with our employee and her family at this time,” hospital spokesman Joe Klimavich said in a statement.

O’Regan is due to be arraigned in Dudley District Court Thursday morning, where he will face a dangerousness hearing and undergo a mental health evaluation.

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WBZ NewsRadio 1030’s Lana Jones reports