PLAINSBORO - Three people were injured, one of them critically, after an explosion inside a patient's room at University Medical Center of Princeton.

The explosion sparked a brief fire at around 8:50 p.m. Investigators believe it was accidental and caused by an oxygen tank.

A nurse was seriously injured in the explosion. She was flown to St. Barnabas Medical Center in Livingston, where she is listed in critical condition. The patient and a visitor in the room were treated for smoke inhalation.

The explosion happened in a room on the third floor in the east wing, causing some windows to shatter.

At least 18 patients in the unit were relocated to the hospital's west wing. No other injuries were reported.

The investigation into the explosion continues.