OTTAWA (Reuters) - Canada’s left-leaning New Democratic Party (NDP), which stormed to victory in a provincial election in conservative Alberta this month, has vaulted ahead of Justin Trudeau’s Liberal Party in national support, a public opinion poll showed on Thursday.

New Democratic Party leader Thomas Mulcair delivers a speech to his caucus on Parliament Hill in Ottawa January 15, 2015. REUTERS/Chris Wattie

The NDP displaced the Liberals in the 2011 election as the official opposition to the governing Conservatives, but the Liberals have been ahead of the NDP in most national polls since Trudeau, son of former Prime Minister Pierre Trudeau, became Liberal leader in 2013.

The new survey by polling company Ekos puts the Conservatives at 30.0 percent support, the NDP at 29.1 percent, and the Liberals at 27.0 percent. Earlier, preliminary, results had put the NDP narrowly ahead of both parties.

Being competitive with the Liberals is critical for the NDP as it vies to be the main alternative to the Conservatives, led by Prime Minister Stephen Harper, in the Oct. 19 federal election.

The federal New Democrats, who have pledged to raise corporate tax rates, eliminate preferential treatment of stock options and introduce cheap national day care, got wind in their sails when their provincial counterparts overthrew the Progressive Conservatives, in power for 44 years, in oil-rich Alberta on May 5.

“There are clear echoes here of last week’s shocking upset in the Alberta election, but it would be a mistake to see the NDP’s rise as merely a bounce effect from Alberta,” Ekos pollster Frank Graves said on the website iPolitics, which published the poll.

“In fact, the past four months have shown a clear pattern of growing support for the New Democrats, lifting them up from 18 points in early February to 29 points today.”

Ekos said the polling results could translate into 125 seats of the 338 seats in the House of Commons for the Conservatives, 117 for the NDP and 94 for the Liberals.

Ekos polled 2,177 voters May 6-12 using an automated phone service, with a margin of error of 2.1 percentage points 19 times out of 20.

The preliminary results that had shown a slight NDP lead were taken from May 6 to 10. The fact that the longer period put the Conservatives narrowly back on top suggests a slight tailing-off of NDP support May 11-12.