An American Airlines flight bound for Dallas from Chicago was forced to make an emergency landing after a passenger tried to open the emergency exit door while in the air. 

American Airlines Flight 2300 left O'Hare International Airport Tuesday and was less than 45 minutes into its flight to Dallas/Fort Worth International Airport when the plane had to be diverted to St. Louis, Missouri, because of the unidentified "unruly passenger," the airline said in a statement Wednesday.

"He started coming at the door," passenger Jonathan Cowan told ABC News. "He just had these big, black gazing eyes. There was really no emotion. ... He had all the door levers being flipped up. He was just going at it, attacking it."

Airline experts said the man couldn't get the exit open, however, because emergency doors are kept sealed during flight by cabin pressure inside the plane.

Others on board were quick to subdue the unruly passenger.

"I got him to the ground, pinned him," Cowan said. "A couple other gentlemen got on back of me and helped pin him down."

Another passenger said that after the man attempted to open the exit door, passengers were the first to take action and then flight attendants assisted.

"The aircraft landed safely and law enforcement met it upon arrival," American Airlines said in its statement. "There were no injuries to passengers or crew members. We thank our crew members for their quick action to ensure the safety of everyone on board and providing excellent care to our customers during a difficult situation."

The man was tied up and held down until the plane landed in St. Louis. Video shared by passengers showed the unidentified man being detained by authorities and later removed from the aircraft in St. Louis.

An FBI spokesman in St. Louis said that the agency had coordinated with airport police during the incident and that no one had been arrested. The man was released without charges.

"There was no nexus to terrorism or criminal activity," the spokesman told ABC News on Wednesday.