Six students have been killed by a gunman who opened fire in a crowded lecture theatre at Northern Illinois University near Chicago in the US.

Another 15 people were injured as the black-clad gunman fired two handguns and a shotgun during a science lecture, before taking his own life.

Eyewitnesses have described scenes of panic as students dropped to the floor of the auditorium or ran for their lives.

Police were at the scene within minutes, but the attacker, a former sociology student at the university, was already dead by the time they arrived.

Emergency workers wheeled the victims on stretchers through the snow to waiting ambulances.

The injured, including the class lecturer, were taken to a local hospital, where concerned relatives arrived to wait for news.

Shocked students were offered counselling and urged to telephone their parents.

Students and staff at the university held vigils to mourn dead friends and colleagues and pray for the survivors.

It was the fourth shooting at a US educational establishment within a week.

All classes scheduled for Friday were suspended, while police stepped up security around the deserted buildings.