A woman from Sri Lanka and her four children were stabbed to death in a home in Ottawa by a student who is also from Sri Lanka, the police said on Thursday. Another man living in the home was also killed, and the children’s father was hospitalized with injuries.

Investigators charged Febrio De-Zoysa, 19, a student who also lived in the home, with six counts of first-degree murder and one count of attempted murder. He was arrested shortly after the police received two emergency calls around 11 p.m. Wednesday requesting they come to the home, which is in a residential neighborhood, police officers said.

Ottawa’s police chief, Eric Stubbs, said at a news conference that the stabbings were the largest mass killing in the city, Canada’s capital, in at least three decades.

“I want to emphasize this was a senseless act of violence perpetrated on purely innocent people,” Chief Stubbs said. “I know our whole community is shocked and mourning this event.”

The victims were identified as Darshani Banbaranayake Gama Walwwe Darshani Dilanthika Ekanyake, 35, the mother of the four children; Inuka Wickramasinghe, a 7-year-old boy; Ashwini Wickramasinghe, a 4-year-old girl; Rinyana Wickramasinghe, a 2-year-old girl; and Kelly Wickramasinghe, a 2-month-old girl.

The children’s father and Ms. Ekanyake’s husband, identified as Dhanushka Wickramasinghe in court documents, was seriously injured in the attack and was in stable condition at an area hospital.

Bhante Suneetha, a monk at the The Hilda Jayewardenaramaya Buddhist Monastery, where the family were active members, said that he spoke by phone on Thursday with Mr. Wickramasinghe, who he said is being hospitalized for slash wounds to his eyes and one of his hands.

Mr. Wickramasinghe told the monk that he arrived home from work on Wednesday night and was attacked when he opened the door, Mr. Suneetha said. Mr. Wickramasinghe was able to subdue his attacker before he discovered the other victims, he said.

Police officers said Mr. Wickramasinghe was seen on the street shouting for someone to call 911.

The sixth person killed, Amarakoonmubiayansela Ge Gamini Amarakoon, 40, was an acquaintance who had recently arrived from Sri Lanka and was living with the family. Mr. Suneetha said that he leaves a wife and two young children in Colombo, the capital of Sri Lanka.

The police said they believed the victims were attacked with “an edged weapon” but did not provide any more details.

According to Mr. Suneetha, Mr. Wickramasinghe arrived on his own in Canada as a student in 2020 and the rest of the family followed about a year ago. After his graduation from college, Mr. Wickramasinghe worked in a restaurant before starting his own cleaning business.

The family, Mr. Suneetha said, came to Canada with so many “dreams and plans.”

“That is why they brought their kids here,” he said.

While he was in school, Mr. Wickramasinghe lived in another Sri Lankan family’s home. Mr. De-Zoysa also boarded there, according to Mr. Suneetha. After that arrangement fell apart, Mr. Wickramasinghe invited Mr. De-Zoysa to live in the basement of his family’s home.

Mr. Suneetha said the family recently celebrated Mr. De-Zoysa’s 19th birthday.

The Wickramasinghe family regularly helped organize events at the temple, and Inuka, the 7-year-old, began his studies in meditation and Buddhism a week ago, Mr. Suneetha said.

Members of the temple were meeting on Wednesday to work out plans for the funerals and to support Mr. Wickramasinghe, as well as the family of Mr. Amarakoon.

Two police SUVs remained parked at the home nearly a full day after the killings. The police chief said it would take several days to process the scene.

Shanti Ramesh, a neighbor, said she saw about 15 police cruisers rush to the home on Wednesday night.

Ms. Ramesh watched as investigators began rolling out yellow crime-scene tape in front of the home. She went to bed thinking the scene would be cleared up overnight.

“But when I saw the news in the morning, it was a shock that such a big tragedy happened in our city and just across my house,” she said, adding that she did not know the family who lived in the home.

Mass killings are rare in Canada, where the homicide rate in 2022 was about 2.3 killings per 100,000 people, about one-third of the rate in the United States that year.

There were 874 murders in Canada in 2022, according to the latest data from the census agency. They represented an 8 percent rise in the country’s homicide rate and the fourth year of consecutive increases.

Mark Sutcliffe, the mayor of Ottawa, offered his condolences.

“We are fortunate to live in a safe city where these events are extremely rare,” he said at a news conference on Thursday afternoon. “Everyone, understandably, will react to this news today and feel less safe and secure.”

About 100 people gathered at a gazebo on the edge of Palmadeo Park, just two blocks from the crime scene, for a memorial vigil on Thursday evening. Some stayed for a while; others stopped only to leave teddy bears, letters or bouquets of flowers.

“They were so sweet, they were caring, they were kind. It was honestly very devastating,” Dayna Craigie, a former educational assistant at the children’s school, said. “I’m remembering them as innocent children who should not have had their lives taken away from them.”

Neela Singh looked on with her two children, ages 4 and 11. They went to school with the victims, she said. Through tears, Ms. Singh described that afternoon’s school pickup as somber.

“There were so many people around, yet no sound until the teacher came out,” she said.

After the peak of the coronavirus pandemic, the temple began holding special counseling and mediation sessions for students from Sri Lanka who, Mr. Suneetha said, seemed to be under ever-increasing stress.

“After the pandemic, the society here in Canada is not so well,” he said.

Recovery, Mr. Suneetha added, will take time for the temple’s 120 members. The temple is a hub for many members of the Sri Lankan community, including several hundred people who are not members of the temple, he said.

“We will definitely need help from the society,” Mr. Suneetha said. “Not just from the Sri Lankan community, but the whole community.”