WASHINGTON - The deadliest school shooting in US history spread shock waves though the United States Monday, reviving calls for tighter gun control and renewing the debate about campus security.

President George W. Bush led expressions of dismay, with spokeswoman Dana Perino saying he was "horrified" by the rampage at Virginia Tech University which left a reported 32 people dead, including the apparent lone gunman in the mass slaying.

"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," Perino said of Bush.

The House of Representatives and Senate both observed a moment of silence for what House Speaker Nancy Pelosi described as a "terrible, terrible tragedy."

Virginia Senator Jim Webb called the carnage a "senseless act" and said his heart went out to the parents and families of the victims.

The state's governor, Timothy Kaine, was cutting short a visit to Japan and said "it is difficult to comprehend senseless violence on this scale."

Gerard Toal, a professor at Virginia Tech, said the incident would deeply affect the staff and more than 28,000 students.

"This is a profound event obviously and it's one that will shake at the core of the university," he told AFP.

He said that the shooting came ahead of the busy exam season, when many students struggled to cope. "There's a lot of pressure on people, we're all feeling the pressure," he said. "Obviously the scale of this is shocking."

"You're dealing with the state of Virginia where there is a strong gun culture and you're dealing with a campus environment," he said. "There are lots of guns around on campus because there is a corps of cadets."

The mass shooting came almost eight years after the shootings at Columbine High School, in which 15 people were killed, and six months after a shooting at an Amish school in Pennsylvania in which six people died, including the gunman.

"Since these killings, we've done nothing as a country to end gun violence in our schools and communities," Paul Helmke, president of the Brady Campaign to Prevent Gun Violence said in a statement.

"If anything, we've made it easier to access powerful weapons," he said. "It is long overdue for us to take some common-sense actions to prevent tragedies like this from continuing to occur."

Ladd Everitt of the Coalition to Stop Gun Violence said that such shootings cast a dark shadow over the entire country.

"We still live in a society where gun violence is an overriding concern," he said. "We've had a series of these high-profile, very violent shootings that have taken a lot of victims.

"In the last year alone we've had a lot of these shootings and we continue to lose more than 30,000 people every year in this country to gun violence."

His organization campaigns for "sensible" gun laws, focusing on closing loopholes that allow people to get hold of weapons without background checks.

Helen Stubbs, associate director of the Higher Education Center, which help sschools tackle violence and drugs on campus, said it was difficult for campuses to have watertight security because they were often so spread out.

High schools, which in the United States often feature metal detectors at entrances, were more contained environments where security could be better monitored, she said.

Ian Ehrenberg, whose company Nice Vision specializes in school surveillance systems, said Monday's shooting proved that there was insufficient security on some school campuses.

"I do think they should do more and I don't think anyone will have a question about that," he said. "It's the responsibility of the school to provide a safe environment for the students on the campus."

"I expect colleges and campuses in the US to increase their security systems after this horrible incident," he said.

Agence France-Presse