Updated

At least 32 people are confirmed dead and at least another 21 are wounded after a shooting at Virginia Tech University Monday morning, federal law enforcement officials told FOX News.

Campus police said there was only one shooter and he is now dead. They are unsure if the shooter was a student and it was unclear if he was shot by police or took his own life.

"The university was struck today with a tragedy of monumental proportions," Virginia Tech President Charles Steger said during a press conference shortly after noon. "The university is shocked and horrified that this would befall our campus ... I cannot begin to convey my own personal sense of loss over this senselessness of such an incomprehensible and heinous act."

It was the deadliest campus shooting in U.S. history.

Steger said school officials are notifying victims' next of kin, and state police and the FBI are still investigating the various crime scenes. They are still trying to identify all the victims. The university will set up counseling centers for students and faculty.

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At 7:15 a.m. Monday, a 911 call came in to the campus police department concerning an incident at West Ambler Johnston, a residence hall, and that there were multiple shooting victims, Steger said. While that investigation was underway, a second shooting was reported in Norris Hall, located at the opposite end of the 2,600-acre campus.

Virginia Tech Police Chief Wendell Flinchum said at least one person was killed at West Ambler Johnston, a residence hall, but several others were injured in that shooting. At least 20 were killed in classrooms in Norris Hall, an engineering building, Flinchum said.

Flinchum said the Norris Hall gunman was dead, but wouldn't say whether the shooter killed himself.

A spokeswoman at Montgomery Regional Hospital said 17 students were being treated there for gunshot wounds and other injuries, and Carilion New River Valley Medical Center in Christiansburg reports that four people with gunshot wounds were being treated there. Carilion spokeswoman Sharon Honaker said one was in critical condition and three others were stable.

President Bush was "horrified" of news of shooting rampage at Virginia Tech, said White House spokeswoman Dana Perino. The White House is monitoring the incident. Local NBC affiliate WSLS reported that Virginia Gov. Tim Kaine, who was heading for a meeting in Tokyo, Japan, for a two-week trade mission, is now returning to the United States.

Virginia Tech's Web site earlier said one shooter was in custody and officials searched for a second shooter as "part of routine police procedure," but during the press conference Monday, police said they believe there was only one shooter.

Police also said there is no evidence that the two shootings at opposite ends of campus were related.

Virginia Tech student Blake Harrison said he was on his way to class near Norris Hall when he saw chaos.

"This teacher comes flying out of Norris, he's bleeding from his arm or his shoulder ... all these students were coming out of Norris trying to take shelter in Randolph [Hall]. All these kids were freaked out," Harrison said.

The students and faculty were barricading themselves in their classrooms after what one person described as an Asian student wearing a vest opened fire.

The shooter was "wearing a vest covered in clips was just unloading on their door, going from classroom to classroom … they said it never seemed like it was going to stop and there was just blood all over," Harrison said.

Matt Merone, a campus senior, was on his way to campus Monday morning when he saw a police officer grab a male student who was bleeding from his stomach area and put him into a vehicle, which whisked him away. He told FOX News that his roommate saw the first shooting.

Student Amanda Johnson was walking between Norris and Randolph halls around 9:45 a.m. when she heard six shots fired.

"I've been target shooting since I was a little kid so I knew what the sounds were," said Johnson, who saw a male student jump out of a Norris Hall window to escape. She and others helped him get into a car.

The campus newspaper reported that because of serious wind, helicopters could not be used to transfer the injured. Ambulances were being used to transport the victims to nearby hospitals.

The FBI joined police on the scene to investigate.

Senior official with the Bureau of Alcohol, Tobacco, Firearms and Explosives told FOX News that agency's response to the Virginia Tech incident was "immediate," and the bureau is making all of its local and national resources, including its crimes lab, available to the Virginia State Police.

Ten ATF agents are now on the Virginia Tech campus assisting with weapons identification. They are collecting shell casings and running some preliminary tests on scene. Once the weapon has been identified, they will begin an "urgent trace" to determine its origins — where it came from, to whom it was registered, and its history of ownership. All material will be sent to the ATF's national crime lab in Maryland.

The ATF is also assisting with "forensic mapping" of the crime scene — a painstaking process employed by investigators that 'maps out' the scene and incident in minute detail.

Many students described the events, saying they were receiving reports of the shootings from the school via e-mail, and that there were announcements telling everyone to stay inside.

"There are police driving throughout the neighborhoods with a loudspeaker saying, 'this is an emergency, everyone stay inside, we're looking for suspicious activity," Brittany Sammon, a senior Virginia Tech student staying at an apartment off campus, told FOX News on Monday. "There's no one outside at all, there's no traffic, there's nothing … everyone's doing what they said."

Sammon, who has a brother and roommate confined to their buildings on campus, said she first got the e-mail from the school regarding the shooting at 9:30 a.m. Monday.

"It was just very short and brief and kind of scary, because it didn't have any details at all in it," she said. "It's definitely nerve wracking."

All classes have been canceled and students and most faculty have been told to stay inside. Tuesday classes have also been canceled but the campus will open at 8 a.m. EDT. Faculty and staff on the Burruss Hall side of the campus drillfield are being released and asked to go home effective immediately. Faculty and staff on the War Memorial Hall side of the drillfield are asked to leave at 12:30 p.m.

Families wishing to reunite with students are suggested to meet at the Inn at Virginia Tech. School officials are making plans for a convocation Tuesday at noon at Cassell Coliseum.

Anyone who observes anything suspicious or has information about this case is encouraged to contact the Virginia Tech Police at (540) 231-6411.

Virginia Tech has the largest full-time student population in Virginia, with more than 25,000 students. It consists of eight colleges and graduate school and offers 60 bachelor's degree programs and 140 master's and doctoral degree programs.

The main campus includes more than 100 buildings located on 2,600 acres, and includes an airport.

Last August, the campus was closed when an escaped jail inmate allegedly killed a hospital guard and a sheriff's deputy involved in a massive manhunt. The accused gunman, William Morva, faces capital murder charges.

On April 13, the campus closed three of its academic halls after they received a letter stating that explosive devices were in the building. Classes were canceled for the remainder of the day. A bomb threat was also made against Torgerson Hall on April 2.

"For some reason, this just seemed a little different … it was more than just a sick joke someone was playing," one student told FOX News about those bomb threats.

This is a developing story. Please refresh your page for updates.

FOX News' Ian McCaleb and The Associated Press contributed to this report.