BLACKSBURG, Va. (AP) — A gunman opened fire in a Virginia Tech dorm and then, two hours later, in a classroom across campus Monday, killing at least 30 people in the deadliest shooting rampage in U.S. history, government officials told The Associated Press. The gunman was killed, bringing to death toll to 31.

“Today the university was struck with a tragedy that we consider of monumental proportions,” said Virginia Tech president Charles Steger. “The university is shocked and indeed horrified.”

It was not immediately clear whether the gunman was shot by police or took his own life. His name was not released, investigators offered no motive for the attack. It was not known if the gunman was a student.

The shootings spread panic and confusion on campus, with witnesses reporting students jumping out the windows of a classroom building to escape the gunfire. SWAT team members with helmets, flak jackets and assault rifles swarmed over the campus. Students and faculty members carried out some of the wounded themselves, without waiting for ambulances to arrive.

The massacre took place at opposite sides of the 2,600-acre campus, beginning at about 7:15 a.m. at West Ambler Johnston, a coed dormitory that houses 895 people, and continuing at least two hours later at Norris Hall, an engineering building about a half-mile away, authorities said.

Police said they were still investigating the shooting at the dorm when they got word of gunfire at the classroom building.

After the first shots were fired, students were warned to stay indoors and away from the windows. But some students said they thought the precautions had been lifted by the time the second burst of gunfire was heard, and some bitterly questioned why the gunman was able to strike a second time, two hours after the bloodshed began.

“What happened today this was ridiculous. And I don’t know what happened or what was going through this guy’s mind,” student Jason Piatt told CNN. “But I’m pretty outraged and I’ll say on the record I’m pretty outraged that someone died in a shooting in a dorm at 7 o’clock in the morning and the first e-mail about it — no mention of locking down campus, no mention of canceling classes — they just mention that they’re investigating a shooting two hours later at 9:22.”

He added: “That’s pretty ridiculous and meanwhile, while they’re sending out that e-mail, 22 more people got killed.”

FBI spokesman Richard Kolko in Washington said there was no evidence to suggest it was a terrorist attack, “but all avenues will be explored.”

Up until Monday, the deadliest mass shooting in U.S. history was in Killeen, Texas, in 1991, when George Hennard drove his pickup into a Luby’s Cafeteria and shot 23 people to death, then himself.