• NEW: Police chief says at least 22 people are dead, including gunman • NEW: Attacks mark deadliest school shooting in U.S. history • Officials tell AP that more than 20 people were wounded • Student describes situation as "mayhem"; says 2 students jumped from window Adjust font size: (CNN) -- A lone gunman is dead after police said he killed at least 32 people Monday during twin shootings on the Virginia Tech campus -- the worst school shooting incident in U.S. history. "Some victims were shot in a classroom," university police Chief Wendell Flinchum said during a news conference in Blacksburg. Police believe there was only one gunman, Flinchum said. "Today the university was struck with a tragedy that we consider of monumental proportions," said university President Charles Steger. "The university is shocked and indeed horrified." (Map of Blacksburg) The shootings mark the deadliest school shooting incident in U.S. history, topping attacks at Columbine High School in 1999 and at the University of Texas in 1966. The Associated Press quoted officials saying more than 20 people were wounded. A hospital spokeswoman told AP that 17 Virginia Tech students were being treated for gunshot wounds and other injuries. Sharon Honaker at the Carilion New River Valley Medical Center in nearby Christiansburg, Virginia, told CNN that four patients had been transported there, one in critical condition. One person was killed and others were wounded at multiple locations inside a dormitory about 7:15 a.m., Flinchum said. Two hours later, another shooting at Norris Hall, the engineering science and mechanics building, resulted in multiple casualties, the university reported. (Campus map) The first reported shooting occurred at West Ambler Johnston Hall, a four-story coed dormitory that houses 895 students. The dormitory, one of the largest residence halls on the 2,600-acre campus, is located near the drill field and stadium. Amie Steele, editor-in-chief of the campus newspaper, said one of her reporters at the dormitory reported "mass chaos." The reporter said there were "lots of students running around, going crazy, and the police officers were trying to settle everyone down and keep everything under control," according to Steele. (Watch police, ambulances hustle to the scene ) Kristyn Heiser said she was in class about 9:30 a.m. when she and her classmates saw about six gun-wielding police officers run by a window. "We were like, 'What's going on?' Because this definitely is a quaint town where stuff doesn't really happen. It's pretty boring here," said Heiser during a phone interview as she sat on her classroom floor.