A state trooper was treated for “serious but non-life-threatening” injuries Monday after being shot in Westbrook in a gunfire exchange with two suspects fleeing the scene of an armed robbery in Old Saybrook.

One of the suspects has died. The other is being treated for injuries at Hartford Hospital.

Police spokeswoman Sgt. Donna Tadiello said the incident began in Old Saybrook at about 3 p.m., when town police began pursuing the suspects after a report of an armed robbery at an undisclosed location. At the request of town police, state police provided assistance and pursued the suspects when they crossed over the town line into Westbrook on Route 153. Both the suspects’ vehicle and the state police vehicle then crashed on Route 153 between Docs Hill and Pettipaug roads and the trooper and suspects exchanged gunfire, Tadiello said. The circumstances of the crash are under investigation.

Another state police trooper arrived on the crash scene and took the injured trooper to the Middlesex Hospital Shoreline Medical Center, about two miles away. The two suspects were also taken to the medical center in separate ambulances. One of the suspects was declared dead on arrival, and the surviving suspect was taken by Life Star helicopter to Hartford Hospital, Tadiello said. No information was available about the surviving suspect’s injuries or condition. The body of the deceased suspect has been sent to the Office of the Chief Medical Examiner for an autopsy.

Tadiello said the injured trooper, described only as a veteran male officer, is expected to recover. His family has been notified. The location of the barracks where the trooper was assigned was not being released.

A section of Route 153 around the crash scene remained closed for several hours Monday afternoon while the police investigation continued. Old Saybrook and state police are also conducting an investigation at the Day’s Inn on Boston Post Road and have taped off the driveway.

Owners of nearby businesses said they did not see or hear anything. A registered guest from Pennsylvania was told he would not be able to return to his room for several hours.

Old Saybrook Police Chief Michael Spera said he could not comment.

Day staff writer Karen Florin contributed to this report.