At least 33 people were killed and more than two dozen wounded at Virginia Tech university yesterday in the deadliest campus shooting in US history.
The rampage by what police believed was a lone gunman took place in two separate areas about two hours apart. Students who had begun crisscrossing the large campus for morning classes rushed for cover.
"This is a tragedy of monumental proportions," Virginia Tech president Charles Steger told reporters.
Virginia Tech campus police chief Wendell Finchum said the suspected gunman was dead and that police were trying to determine whether he killed himself or was shot by officers.
"At this time we believe it's only one gunman," said police chief Finchum.
President George W. Bush was "horrified" by the shooting.
"He was horrified and his immediate reaction was one of deep concern for the families of the victims, the victims themselves, the students, the professors and all of the people of Virginia who have dealt with this shocking incident," a White House spokesman said.
A student journalist's video of the chaos was replayed repeatedly on US television networks, showing people scurrying around the campus and volleys of shots ringing out.
The death toll was worse than a massacre at the University of Texas in Austin on August 1, 1966, when trained marksman Charles Whitman killed 15 people, including his mother and wife the night before, and wounded 31 others.
The first shooting at Virginia Tech, a state university, was reported to campus police at about 7:15 a.m. (1115 GMT) in West Ambler Johnston Hall, a dormitory housing some 900 students.
It was followed by more shooting at Norris Hall, site of the science and engineering school that has given the university much of its fame as a leading technical institute in the US.
The wounded were taken to hospitals in the area for treatment.
Students told CNN there were multiple bomb threats to the campus last week. Two of the threats were aimed at the science and engineering school.
Virginia Tech, with 26,000 students, is located in the town of Blacksburg and set in lush rolling hills in the southwest corner of the state, about 390 km from Washington.
"It's just shock and anger around here right now," graduate student Elizabeth Stewart told CNN, adding she saw the shootings as "freak incidents" that would not stop her attending Virginia Tech.
"I love my school with all my heart and soul."
The university had already sent out an e-mail canceling classes after the first shooting when students heard more shots, another student, Laura Spaventa, told CNN.
Classes were cancelled and counsellors were being brought in to talk to the students.
"We continue to work to identify the victims that have been impacted by this tragedy," said Mr Steger, the university president.
"I cannot begin to convey my own personal sense of loss over this senseless and incomprehensible heinous act."
Virginia Tech closed for a day last August 21 because of a manhunt for an escaped prisoner. William Morva, accused of shooting and killing a hospital guard and then a sheriff's deputy near the Virginia Tech campus while on the run, was captured a day after escaping custody on August 20.
US News & World Report, which produces well-regarded annual ratings of US universities, ranked Virginia Tech's College of Engineering 17th for an engineering school in the United States, tied with Rensselaer Polytechnic Institute, Texas A&M University, and the University of Minnesota.
The killings at Virginia Tech university yesterday will stir fresh US debate over gun control and what drives people to go on shooting rampages through schools and colleges.
Last October, a gunman shot 10 Amish girls at a one-room schoolhouse in Pennsylvania, killing five before turning the gun on himself.
In April 1999, teenagers Eric Harris and Dylan Klebold, armed with guns and homemade bombs, killed 12 fellow students and a teacher at Columbine High School in Colorado in a long-planned spree.
School shootings have prompted changes to school safety rules and sparked debate over the availability of guns.
They also have prompted an outpouring of academic studies on the causes of stress, depression and violence in young people and novels such as the award-winning "We Need to Talk About Kevin" by Lionel Shriver, about a school massacre.
People who commit killings in schools and colleges are sometimes motivated by a specific grievance against that institution or people within it, said Nadine Kaslow, a professor and chief psychologist at Emory School of Medicine.
They are sometimes mentally ill and may equally be reacting to a trauma, either real or imagined, that they have suffered, and decide to take that trauma out on everyone else, Ms Kaslow said in an interview.
"Some of these people - I don't want to use the word 'snap' - but they just go over the edge. All the rest of us have a conscience that says: 'don't do this,'" she said stressing she was new to the Virginia Tech case.
The way in which the media play up cases such as Columbine may make the idea of committing such a crime to achieve notoriety attractive to certain individuals, she said to explain why such killings appear more prevalent in the US than in other Western countries.
Advocates of wider gun controls said the availability of guns in the US had made it easier for people to commit murder everywhere, including in schools and colleges.
"What have we done as a nation in the eight years since Columbine about this problem? We compound the trade of the day by our failure to deal with the proliferation of guns in our country," said Paul Helmke, president of the Brady Centre to Prevent Gun Violence.
Mr Helmke said that since Columbine, which happened eight years ago this week, there had been no new legislation on control of guns and he said a ban on assault weapons was allowed to expire in September 2004.
Advocates of gun freedom such as the National Rifle Association argue that the right to bear arms is enshrined in the US constitution and dispute efforts to link the incidence of gun crime with access to firearms.