A black-clad man fired into a lecture hall packed with students at an Illinois university on Thursday, killing five people and wounding 18 before shooting himself dead, police and college officials said.

The gunman, who police said had a shotgun and two handguns, stepped onto the lecturer's stage near the end of a mid-afternoon geology class at Northern Illinois University and began shooting down the room, sending terrified and bleeding students fleeing, witnesses said. He then shot himself on the same stage.

Police on the 25,000-student college 65 miles west of Chicago said the gunman was a former student but they did not publicly identify him and said they did not know the motive in the latest in a series of shootings at U.S. colleges and high schools.

University President John Peters said there had been a "very brief rapid fire assault that ended with the gunman taking his own life." He said those killed by the gunman were all students -- four women and one man -- and that 4 were in critical condition in hospitals. The instructor teaching the class survived, he said.

"I ducked behind the seats and ran out the door," student Zach Seward told the local Daily Chronicle newspaper.

"As I was running, I just kept waiting for something to hit me in the back. I didn't know where to run, tried to decide where it's safe to be, and there isn't anywhere safe."

FORMER STUDENT

Peters said the gunman was a sociology major who last attended classes as a graduate student in the spring of 2007 and who may have since enrolled at a different college. He said he had no police record or previous contact with police.

One student told local radio that roughly 140 students were in the classroom when the man opened fire. Ambulances swarmed onto the snow-covered campus and classes were canceled for the rest of the day and Thursday.

"Some girl got hit in the eye, a guy got hit in the leg," George Gaynor, a student who was in the hall told the Northern Star, the student newspaper on the campus.

Kristina Balluff, a student, said the gunman was dressed in black pants and had fired randomly from the raised classroom stage.

"I looked at this girl next to me and actually said, 'is this real?' I think the professor ... ducked out of the way."

Mass shootings are not rare in the United States, where gun control is less strict than in many countries and where the gun-ownership lobby is politically influential.

A university in Blacksburg, Virginia, Virginia Tech, became the site of the deadliest shooting rampage in modern U.S. history in April last year when a gunman killed 32 people and himself.

Last week, a nursing student shot dead two women and killed herself in front of horrified classmates at a college in Louisiana.

In December, a threat was found scrawled on a wall at Northern Illinois University referring to the Virginia shooting and threatening similar violence, but officials said they had no reason to link that to Wednesday's incident.