Chicago, Illinois - A United Airlines flight from Newark to Los Angeles was forced to make an emergency landing in Chicago Wednesday morning after a threatening note was discovered in the plane’s bathroom, police said.

United Airlines Flight 1533, packed with more than 200 travelers, lifted off from Newark Liberty International Airport around 6:05 AM, CBS News reported.

It was due to arrive at Los Angeles International Airport before 10 AM, but the pilot suddenly had to change course after crewmembers reported a "Level Two" safety threat.

The plane made an emergency landing and touched down at O’Hare International Airport in Chicago around 7:40 AM.

Witnesses and law enforcement sources told ABC News that a passenger scuffled with crewmembers mid-air.

A bomb threat was found written on a note in the plane's bathroom a short time later.

Police confirmed the Boeing 787 was evacuated upon arrival at O'Hare International, where authorities combed through the aircraft in a safe location.

A bomb-sniffing K9 reportedly uncovered a suspicious bag during their search, and a robot was deployed to move it.

An airline source said the dog connected a scent from the bathroom note to the bag.

"They are taking us back to a terminal. I guess they will go through bags, maybe question us," one passenger, who was not named, told CBS late Wednesday morning.

"We were forced to leave all of our stuff on the plane and have no idea what is happening next."

The passenger who checked the seemingly suspicious bag is being questioned by police and the FBI said it is currently investigating the situation.