Six people from Sri Lanka, including a mother and four young children, were knifed to death in the Canadian capital Ottawa late on Wednesday, police said on Thursday, rocking a country where mass murders are rare.

Prime Minister Justin Trudeau said he was horrified by what he called a "terrible tragedy." The father of the family was also wounded in the attack and is in hospital.

Police said Febrio De-Zoysa, a 19-year-old male student from Sri Lanka, had been arrested and charged with six counts of first-degree murder and one count of attempted murder. De-Zoysa knew the family and had been living in the house, they said.

The victims killed were a 35-year-old woman and her children aged 7, 4, 2 and 2 months, as well as a 40-year-old man who was an acquaintance of the family.

"This was a senseless act of violence perpetrated on purely innocent people," Ottawa police chief Eric Stubbs told a televised news conference. Police said they had had no previous dealings with the suspect or the family.

Ottawa Mayor Mark Sutcliffe, in a social media post, said it was "one of the most shocking incidents of violence in our city's history".

Ottawa, which has a population of one million, saw 14 murders in 2023 and 15 in 2022.

Wednesday's victims were found inside a house in the southwestern suburb of Barrhaven. Police arrived on the scene following emergency calls shortly before 11 pm on Wednesday.

Mass killings in Canada are infrequent. In December 2022, a man shot five people in a Toronto suburb before being gunned down by police.

In September that year, a man stabbed and killed 11 people in the western province of Saskatchewan. He died of a cocaine overdose shortly after being arrested.