Prime Minister Stephen Harper is expected to call several byelections on Sunday to fill four vacancies in the House of Commons (Sean Kilpatrick/Canadian Press)

Prime Minister Stephen Harper is expected to call four byelections on Sunday to fill vacant seats in the House of Commons.

The byelections would be held for two vacant seats in Quebec, one in British Columbia and one in Nova Scotia.

The Quebec seats in Montreal and the eastern Quebec region of Rivière-du-Loup are considered Bloc Québécois strongholds, with the Bloc party candidates winning well over half the votes in 2008.

The Nova Scotia riding was held by independent MP Bill Casey, a former Conservative MP who was ejected from the caucus after he broke ranks and voted against a bill to implement the federal budget. He was re-elected as an independent but has since resigned his seat.

The B.C. seat was held by former New Democrat MP Dawn Black, who left to run for a seat in the provincial legislature.

Black beat her Conservative candidate by more than 1,000 votes in last October's federal vote. The Tories held the riding as recently as 2004.

The byelection call comes as recent opinion polls put the Tories ahead of the Liberals by at least six points.

Harper's minority government survived a Liberal no-confidence motion last week with help from the NDP, averting an election.

The Liberal motion was defeated after the NDP decided to abstain.

NDP Leader Jack Layton had earlier said his party is propping up the Conservative government to ensure the speedy passage of legislation extending employment insurance benefits.

With files from The Canadian Press