MONTREAL - Firecrackers, not gunshots, sparked a massive floor-by-floor search by shotgun-toting police inside a Montreal university Thursday as officers hunted for a man believed to be armed.
  
Students remained holed up in classrooms for several hours at the Universite du Quebec as dozens of officers in bulletproof armour scoured the school.

Police Cmdr. Alain Simoneau said investigators found no evidence that a gun had been discharged inside the building and police had no suspects.

He said police did find spent firecrackers inside a school elevator.

Investigators also found an abandoned bag containing two knives and several unused 22-calibre bullets.

"We didn't see any panic among the students, we didn't see anyone with a gun," Simoneau said.

"We haven't found anything that suggests there was any gunfire."

He would not describe the knives or say if the bag, found near a classroom, was connected to the firecrackers.

Police are examining images taken by a surveillance camera that show a nervous-looking man holding the bag, Simoneau said.

Officers rushed to the university at 1:45 p.m. after six people at the school called 911 to report hearing gunfire inside the building.

More than 30 police cruisers surrounded the university and officers cordoned off several blocks, snarling traffic in the city's core.

Paramedics said three people inside the building were treated for shock.

Outside the building, nervous students huddled in the cold as police raced into their school.

Some said when they saw police in the hallways, hands on their holstered sidearms, they immediately thought of the shooting at Montreal's Dawson College.

A gunman killed one student and wounded about 20 others at Dawson in September 2006.

"(Someone) was killed at Dawson, so I was like 'I don't want to be killed,"' said student Julie-Catherine Pilon.

"We heard some people (in the halls) who were like, 'Someone is shooting."'

Jonathan Hille, 22, said the Dawson attack also popped into his head.

"We thought this is like Dawson," he said. "I was pretty worried because a lot of my friends were studying for exams when this happened."

The communications student said he heard an intercom message telling students to stay in their classrooms.

"Then I saw 20 policemen and I thought 'This is a big deal,' " Hille said.

School maintenance worker Pierre Laxon said he alerted security when he spotted the sports bag and noticed some bullets on top of it.

Laxon said he didn't hear any gunshots.

"I didn't panic," he said.

Edwin Cedeno, 36, said he heard a bang but didn't think much of it.

"It sounded like firecrackers," said Cedeno, an administration student.

Sebastian Dufresne, a third-year student, was in a classroom about to start an exam when he heard a loud noise.

"Just before two o'clock, we heard gunshots, or what sounded like gunshots," Dufresne said.

"I was able to get out of class ... no one said we couldn't go out.

"I went to get a juice and then when I returned a police officer told me to back up."

Dufresne said he heard about five or six shots coming from the basement level.

Thursday's police operation also stirred memories of the deadly rampage at Montreal's Ecole Polytechnique in December 1989.

Last weekend marked the 19th anniversary of the slayings when gunman Marc Lepine stormed the school and killed 14 women.