More than 30 people were injured Monday morning when a Chicago Transit Authority train jumped the platform and climbed up an escalator at the end of the Blue Line at O’Hare International Airport, officials said.

“I heard a boom and when I got off the train, the train was all the way up the escalator. It’s a wreck,” Denise Adams, who was riding toward the back of the train, told reporters. “It was a lot of panic because it was hard to get people off the train.”

Fire crews scrambled to determine if anyone was underneath the train but no one was found, according to Chicago Fire Commissioner Joe Santiago. All of the injured were aboard the train and were taken in fair or good condition to four hospitals, he said. The operator of the train “was walking and talking as we were investigating,” Santiago said.

The eight-car train was wedged near the top of an escalator used by commuters at the Blue Line terminal. CTA spokesman Brian Steele said workers may have to cut up the car and remove it piece by piece, which could take 12 to 24 hours. Then the damage will have to be assessed and repairs made before trains use the station, he said.

In the meantime, shuttle buses will be used between Rosemont, Ill., and O’Hare.

Steele said the cause of the accident remained under investigation. “We don’t know yet what led to this incident. … We will be looking at everything — equipment, signals, the human factor, any extenuating circumstances,” he said.

Steele did say the train was “apparently traveling at a higher rate of speed than a train would be” while pulling into the station, and officials are trying to determine why. He said the National Transportation Safety Board was also investigating.

The president of a Chicago transit union said Monday there are indications that the operator dozed off.

According to the Associated Press, the train operator told Amalgamated Transit Union Local 308 President Robert Kelly that she had worked a lot of overtime recently and was “extremely tired” at the time of the derailment, Kelly said at a news conference.

The accident happened around 2:50 a.m. “There is a stop down there for each track. There’s three tracks there. The train actually climbed over the last stop, jumped up the sidewalk and went up the escalator,” Santiago said.

More than 50 firefighters and paramedics responded, he said. “We did not know if there was anyone underneath the train … so we brought in our specialized units to check underneath there. … They made a visual to make sure no one was underneath.”

Kelly said the operator suffered minor injuries to her leg.

The operator will undergo drug and alcohol tests as part of standard procedure, Steele said.

Initial inspections indicate that the front two cars of the train were damaged, as well as the escalator, officials said.

“Once we remove the train, we’ll have a much clearer picture of what the issues are there,” said Chris Bushell, chief infrastructure officer for the CTA. “At this moment, it looks like we have significant damage to one escalator.”

While there was some structural damage to the platform as well, “the stairs look solid and the majority of the rest of the structure underneath looks solid.”

Steele said the accident occurred during one of the lowest traffic times at the station.