The Bloc Québécois has split into warring factions as seven of 10 MPs have left the party to protest the leadership of Martine Ouellet, a separatist hawk who currently sits in Quebec's National Assembly.

The party now consists of three MPs who support Ms. Ouellet and her unrelenting focus on promoting Quebec secession. The new rump, which remains nameless, is made up of seven MPs who say their priority in the House should be defending Quebec's interests. Departing MPs said Ms. Ouellet was not listening to their concerns.

"I'm really disappointed because we have a responsibility toward the Bloc Québécois, our 20,000 members and the independence of Quebec," Ms. Ouellet said Wednesday.

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Even before the schism, the Bloc caucus was far smaller than at its peak in the early nineties, but it has continued to attract about 20 per cent of the vote in Quebec in recent elections and polls. Its travails stand to leave a number of ridings up for grabs in Quebec in the next election, providing an opportunity particularly for the Conservatives and the NDP to make gains in the province.

The Bloc was created in 1991 by disaffected Liberal and Progressive Conservative MPs after the death of the Meech Lake Accord, which would have brought Quebec into the Constitution. It became the Official Opposition in 1993 and remained a dominant force in Quebec in the 2000s. However, its support has declined in recent years as the party won four seats in 2011 and 10 in 2015.

After separating into two factions on Wednesday, the Bloc is closer than ever to disappearing from Canada's political landscape.

The Bloc has regularly faced internal upheaval over the years, but Louis Plamondon, the dean of the House of Commons, said the party has now hit rock bottom.

"I have seen a number of crises in the Bloc Québécois. There is no doubt this is the biggest," said Mr. Plamondon, who was first elected as a Progressive Conservative in 1984 and now opposes Ms. Ouellet's leadership.

Mr. Plamondon said previous Bloc leaders such as Lucien Bouchard and Gilles Duceppe "always managed to patch things up, but that did not happen in this case."

In an interview, Mr. Duceppe said the writing is on the wall for Ms. Ouellet. "When 70 per cent of a caucus doesn't see its priorities reflected by the leader, he or she has to leave," Mr. Duceppe said. "Secondly, I don't think the Bloc has to choose between promoting sovereignty or defending Quebec's interests. You can do both at the same time, as we used to do."

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Ms. Ouellet, who has been sitting in the National Assembly since 2010 and who is promising to run for the Bloc in 2019, said she will not quit as leader. "I'm staying on," said Ms. Ouellet, who finished third in the Parti Québécois leadership race in 2016 before becoming Bloc Leader last year. "I was elected by Bloc Québécois members; they are the one who gave me my mandate."

Unless Quebec sovereigntists find a way of winning the provincial election later this year, the Bloc vote stands to collapse in the 2019 federal election, pollster Jean-Marc Léger said. He added that among federalist politicians, the biggest victim of the Bloc's unravelling stands to be Prime Minister Justin Trudeau.

"What is obvious is that Bloc voters won't go to the Liberal Party," Mr. Léger said. "The Conservatives are more likely to benefit, along with the NDP to a lesser extent given the left-wing faction in the party. Over all, these are voters who oppose Justin Trudeau."

Still, Mr. Léger said federalists should not confuse the potential disappearance of the Bloc or the PQ's struggles with the looming death of the separatist movement.

"English Canadians like to think that separatism is dead, but it's not true. The PQ's project is facing hard times, but support for sovereignty remains at 36 per cent in the polls," he said.

The potential impact of declining Bloc support in the next general election is hard to gauge because the party usually thrives in ridings that feature unpredictable three- and four-way races. Of the 10 Bloc MPs elected in 2015, seven won with fewer than 35 per cent of the votes.

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Carl Vallée, a Quebec strategist in the Conservative government of Stephen Harper, said Bloc voters will tend to react differently whether they live in Montreal or in the rest of Quebec.

"In rural areas, it could help the Conservatives, because these are what we call 'blue' voters," said Mr. Vallée, now a partner at Hatley Strategies. "On the island of Montreal, there is a direct link between Bloc and NDP voters."

The Bloc was initially designed to act as a temporary sovereigntist front in Ottawa, but it continued to exist after the Yes side lost the 1995 Quebec referendum, keeping the province in Canada. While the party struggled to define its raison d'être in subsequent years, it continued to win strong majorities in Quebec after the sponsorship scandal exposed corruption in Liberal ranks in the early 2000s.

The 2011 election could have spelled the death of the Bloc, when the NDP Orange Wave took over much of Quebec. Mr. Duceppe returned as leader in 2015 and helped the party rebound, but he quit after losing in his riding.

Ms. Ouellet is the sixth Bloc leader. She said on Wednesday that in her tenure, she spent too much time focusing on her political goals and not enough time cultivating personal relations inside the caucus. She added that she offered to go into mediation with MPs to find a new way to elaborate party positions and establish political tactics.

"Sadly, there wasn't much discussion over the proposal," she said after a short caucus meeting that preceded the split. "People stood up and left."

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Former Bloc leader Mario Beaulieu, who is still an MP and supports Ms. Ouellet, said that infighting in the party goes back years. "We have to put our political cause ahead of everything else," he said.

But the MPs who left the Bloc said there was simply no way out of the crisis as long as Ms. Ouellet remained in her role. "The differences that we have with the leader are too important for a lasting peace to be foreseeable," said Mr. Plamondon, surrounded by six other former Bloc MPs. "It is with a wounded heart that we are leaving."