Three suspects were arrested and a fourth reportedly shot himself dead after police surrounded his home.
At least two suspects had intended “to go to a public venue… with a goal of opening fire to kill citizens, and then themselves”, police said.
Police officials said the motive did not appear to be terrorism, without providing further details.
Brian Brennan, commanding officer of the Nova Scotia Royal Canadian Mounted Police, said the plot had involved a 19-year-old man from the Halifax suburb of Timberlea and a 23-year-old woman from the US state of Illinois.
The two, he said, had had access to firearms.
When police went to arrest the 19-year-old man from the Halifax suburb of Timberlea, he killed himself, a senior police official told AP news agency on condition of anonymity.
A 20-year-old Canadian man was arrested along with the woman at Halifax Stanfield International Airport. The fourth suspect, a 17-year-old Canadian boy, was arrested at a house.
The roles of the latter two suspects were still to be determined by investigators, police said.
Brian Brennan said he would describe the alleged plotters as a “group of individuals that had some beliefs and were willing to carry out violent acts against citizens but there’s nothing in the investigation to classify it as a terrorist attack”.
“I can tell you that it’s not culturally based,” he added.
Police believe they have apprehended “all known individuals in this matter and eliminated the threat”, he added.
According to the official who spoke to AP, the man who killed himself had told them he had no guns but he shot himself as he was coming out of the house.
The suspects had been on a chat stream and were apparently obsessed with killing and death and had many photos of mass killing, the anonymous official added.
Steven Blaney, the minister for public safety, said the arrests were a “great example of the fine work they do on a daily basis to help keep Canadians safe”, Canada’s CBC News reports.
kqZQC9xUHwMImage source: Wikimedia Commons President-elect Donald Trump celebrated his election victory at the Ultimate Fighting…
Millions of voters across the US chose to return Donald Trump to the White House…
Donald Trump declares victory in the US election as he addresses jubilant supporters in Florida.…
Stocks around the world are rising as Donald Trump appears to be on the cusp…
Donald Trump has won Pennsylvania, North Carolina and Georgia and taken a lead over Kamala…
Quincy Jones, the celebrated musician and producer who worked with Michael Jackson, Frank Sinatra, Ray…