Claire Papoulias, a Michigan State University sophomore, told NBC's "Today" show Tuesday that she thought she was "going to die" as the shooting unfolded Monday night.

"I could hear gunshots like directly behind my head and I could see the smoke, like gunpowder or something from that weapon firing, and then I could smell – and immediately I dropped to the floor with all my classmates and someone was yelling that there was a shooter and everybody needed to get down on the ground," she said. "And at that moment I thought that I was going to die."

"After I heard those gunshots my classmates in the back of the classroom started to scream for help and my other classmates jumped into action trying to help everyone," Papoulias continued. "If it weren't for my classmates helping everyone I don't think that we would have all made it because immediately someone was like 'we need to break open this window.'"

"The shooter, he came in through the back door... and he just started attacking people and I will never forget the screams of my classmates, they were screaming in pain for help," she added. "After they got the window open, they started to guide people through."

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Michigan State University shooting cleanup

A worker cleans up outside Berkey Hall at Michigan State University, Tuesday, Feb. 14, in East Lansing, Michigan. (AP/Carlos Osorio)

It is not immediately clear what caused gunman Anthony McRae to leave Berkey Hall and head to the school's student union, where he also opened fire.

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Michigan State University shooter Anthony McRae

This booking photo provided by Michigan Department of Corrections shows Anthony McRae. (Michigan Department of Corrections/AP)

But Papoulias says he entered the room and started shooting without warning.

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Students on campus at Michigan State University after shooting

Students gather on the campus of Michigan State University after a shelter in place order was lifted early Tuesday, Feb. 14, in East Lansing, Michigan. (AP/Al Goldis)

"There was a boy in my class and he was waiting outside the window and he was catching people and helping people down," Papoulias also said. "I just grabbed my backpack and my phone, and I remember I just ran for my life. I didn't know where the guy was."

Three Michigan State University students were killed in the attack and five remain in critical condition, police said Tuesday.