MONTREAL — A man in a black trench coat and a mohawk haircut opened fire yesterday at a downtown Montreal college and wounded at least 20 people — eight critically — before police shot and killed him, witnesses and authorities said.

Police dismissed suggestions that race or terrorism played a role in the lunch-hour attack at Dawson College, where scores of panicked students fled into the streets after the shooting began. Some had clothes stained with blood; others cried and clung to each other. Two nearby shopping centers and a daycare center also were evacuated.

“I was terrified. The guy was shooting at people randomly. He didn’t care. He was just shooting at everybody,” a student, Devansh Smri Vastava, said. “There were cops firing. It was so crazy.”

Witnesses said the attacker started firing outside the college before walking in the front door. Much of the shooting was in the second-floor cafeteria, where students dropped to the floor and lay in terror. At times, the gunman hid behind vending machines before emerging to take aim — at one point at a teenager who tried to photograph him with his cell phone. Teachers ran through the halls, telling everyone to leave the building.

Police rushed to the scene, hiding behind a wall as they exchanged fire with the gunman, whose back was against a vending machine, one student, Andrea Barone, who was in the cafeteria, said. He said the officers proceeded cautiously because many students were trapped around the assailant, who yelled, “Get back! Get back!” every time an officer tried to move closer.

Eventually, Mr. Barone said, the gunman went down in hail of gunfire. Authorities did not provide any information about the attacker. A police spokesman, Ean Lafreniere, said the attack involved just one gunman at the school and that the search for any others was over.

Although police initially suggested the gunman had killed himself, Police Director Yvan DeLorme later said at a news conference that, “based on current information, the suspect was killed by police.”

Police with guns drawn stood behind a police cruiser as a SWAT team swarmed the 12-acre campus. The attacker’s bloody body, covered in a yellow sheet, lay next to a police cruiser near an entrance to a school building.

Montreal General Hospital said 11 people were admitted, including eight who were in critical condition. The nine others were taken to two other hospitals.

“Today, we have witnessed a cowardly and senseless act of violence unfold at Montreal’s Dawson College,” Prime Minister Harper of Canada said. “Our primary concern right now is to ensure the safety and recovery of all those who were injured during this tragedy.”

The shooting recalled the 1999 attack at Columbine High School in Colorado, where two students wearing trench coats killed 13 people before committing suicide. Canada’s worst mass shooting also happened in Montreal. Gunman Marc Lepine killed 14 women at the École Polytechnic on December 6, 1989, before shooting himself.

The 25-year-old Lepine roamed the halls of the school firing a rifle, specifically targeting women whom he claimed in a suicide note had ruined his life. Nine women and four men were wounded.

That shooting spurred efforts for new gun laws and greater awareness of societal violence — particularly domestic abuse. Canada’s tighter gun law was achieved mainly as the results of efforts by survivors and relatives of Lepine’s victims.

Dawson is more of a pre-college division than a traditional university. It was the first English-language institution in Quebec’s network of university preparatory colleges when it was founded in 1969. With about 10,000 students, it is the largest college of general and vocational education, known by its French acronym CEGEP, in the province.

Witnesses to yesterday’s attack said a man wearing a trench coat entered the school cafeteria and opened fire without uttering a word. Derick Osei, 19, said he was walking down the stairs to the cafeteria when he saw a man with a gun.

“He … just started shooting up the place. I ran up to the third floor, and I looked down, and he was still shooting,” Mr. Osei said. “He was hiding behind the vending machines, and he came out with a gun and started pointing and pointed at me. So I ran up the stairs. I saw a girl get shot in the leg.”

Mr. Osei said people in the cafeteria were all lying on the floor.

Mr. Barone said that, as they were crawling out toward an exit, they saw a girl who had been shot in the torso and who was face down surrounded by a pool of blood.

He said officers told them: “Don’t look, don’t look. Keep going out.”