CHICAGO (Reuters) - Passengers and crew on board a Chicago-bound flight on Sunday had to subdue a man who tried to open an emergency exit door mid-air, forcing the plane to make an unscheduled landing in St. Louis, authorities said.

No injuries were reported, and the unidentified 43-year-old man from suburban Chicago was taken into custody, they said.

The man tried to open the emergency door on Continental Airlines Flight 546, which originated in Houston and landed safely at about 1:30 p.m. in St. Louis, authorities said.

"Police officers boarded the plane and found the disruptive passenger on the floor near the front of the plane, being detained by a flight attendant and two passengers," said Lambert-St. Louis International Airport spokesman Jeff Lea.

The passenger had apparently left his seat during the flight, saying he had to get off the plane, Lea said.

He was being questioned and had not been charged, authorities said.

The FBI was working with airport officials to investigate what happened, said spokeswoman Rebecca Wu, who would not provide any details.

Aviation experts say it is very difficult, if not impossible, to open the doors of a commercial aircraft during flight because pressurization and the mechanical structure of the doors function to keep them sealed.

(Reporting by Eric Johnson, editing by Ellen Wulfhorst)

Mochila insert follows.