A man killed at least six people and injured at least two others during a stabbing rampage at a popular shopping mall in Sydney, Australia on Saturday afternoon, in one of the country’s deadliest acts of mass violence in recent decades.

The authorities said a man wielding a knife entered the Westfield Bondi Junction shopping center and began stabbing people before a lone police officer shot and killed him. Five people died of their injuries at the scene and one died later in the hospital, the police said. Among those hospitalized, some in a critical condition, was a nine-month-old baby.

Police officials on Saturday did not formally identify the attacker, but said that they believed they knew who he was, and that he had acted alone. His motives were unclear, but they said that the victims did not appear to have been targeted. If their belief about the attacker’s identity is confirmed, they said, the attack was not a “terrorism incident.”

The violence of the rampage, which took place on a weekend in a bustling area popular with families, children and beachgoers, stunned Australians. Mass shootings are rare in the country, which has strict gun laws, and Saturday’s attack was the worst act of mass violence since 2017. In that incident, a driver in a drug-induced psychosis killed six people after deliberately plowing his car into pedestrians in Melbourne.

For many shoppers, the commotion came first, before it was clear that there was danger. Some hid in backrooms fearing for their lives as alarms blared through the mall. Others ran, screaming, passing by the injured victims on the floor. Parents held their children’s hands.

Gavin Lockhart, 37, said in a telephone call that he was sitting in a coffee shop at the mall when he suddenly saw people running. At first, he said, he thought it was a celebrity sighting. Then, he said, he began hearing, “He’s got a knife! He’s got a knife!”

Michael Dunkley, 57, the owner of a coffee shop in the mall, said by telephone that when the screaming began, he had one thought in his mind: “I have to get my wife and staff to safety.” He led the group to a staff room before going out to find the attacker.

Mr. Dunkley said he witnessed a police officer apprehend the attacker on the fifth floor of the mall. He described the attacker as a thin man with a beard and short hair, wearing dark green pants and a green jersey. The officer told him to stop and put the knife down, he said, but then lunged toward her with a knife. “He didn’t say anything,” Mr. Dunkley said. “He seemed determined.”

The officer, a senior policewoman who had been in the vicinity, according to the authorities, then shot the attacker, Mr. Dunkley said, and administered CPR after he fell. The police said the man was fatally shot.

Footage of the attack, shared by local media, captured the knife-wielding man running toward shoppers and the crowd’s screams. One person apparently tried to confront the attacker on an escalator. Other witnesses said that they had used nearby clothing items to compress wounds on a mother and the nine-month-old baby who had been stabbed.

One of those administering treatment to victims was Andrew Reid, 44, a lifeguard who was shopping for a bed when he heard that people had been stabbed. Many stores were in lockdown and people had been ordered to evacuate, he said by telephone. But after seeing people lying bleeding on the floor, Mr. Reid said, he used his lifeguard training to try help them.

One had a wound in her back, he said, adding that they had used clothes from a clothing store to try stem the bleeding. He ran over to another woman who was lying unconscious nearby and had a deep wound on her chest, he said.

“There was a lot of blood around her,” Mr. Reid said. “I honestly don’t think she made it.”

Many of those who were evacuated praised the response of the police. Mr. Lockhart, who said he had seen the officer shoot the attacker, sounded dazed. “The one positive I’m looking at is the police officer probably saved my life,” he said.

Prime Minister Anthony Albanese also praised the courage of the officer who confronted the attacker. “There’s no doubt she saved lives through her actions,” he said at a news conference on Saturday, calling her a “hero.”

Australians, he said, would be shocked. “This was a horrific act of violence indiscriminately targeted at the innocent people going about an ordinary Saturday, doing their shopping.”

Adding to the shock was that the rampage occurred at Bondi Junction, an area east of Sydney better known as a meeting ground for friends and families looking for a day of shopping, or passing through on their way to the beach. Shoppers on any given weekend wander through hundreds of stores at the sprawling mall.

The area is a transit hub for both residents and tourists visiting the sandy beaches of the Sydney’s eastern suburbs. They include some of the city’s most iconic stretches of coastline, such as Bondi Beach.

“In this country, this stuff shouldn’t happen,” said Mr. Dunkley, the coffee shop owner. “People come here because it’s safe.”