The Liberals have won a key provincial byelection in southern Labrador, beating back a challenge from the surging NDP.

With all 25 polls reporting, Liberal Lisa Dempster had 1,141 votes, while the NDP's Jason Spingle had 703.

Tory Dennis Normore trailed well behind with 287.

Liberal candidate Lisa Dempster. (CBC)

"It's humbling, far more humbling than I could have anticipated, to now become a servant, really, for the people of Cartwright-L'Anse au Clair," Dempster told CBC News by phone from her hometown of Charlottetown on Tuesday night.

"They are now my employer. They showed me tonight that they have confidence in me, and I am absolutely looking forward to working for them."

Dempster will become the sixth member of the Liberal caucus in the house of assembly. She replaces Yvonne Jones, who resigned earlier this year to successfully run for a seat in Parliament.

Liberal Liberal Dwight Ball said he was pleased to keep the momentum going from recent poll results that showed the party climbing in support.

"We've been having a few good weeks, I must say," Ball told CBC.

"We're pleased to come out of Cartwright-L'Anse au Clair with a win tonight. But more than that, we're very happy that Cartwright-L'Anse au Clair will get an MHA back now to represent them and address the many issues that we see in the district."

With the victory, the Liberals regain a one-seat edge on the NDP in the legislature.

Big jump in support for NDP, Tories fall to 3rd

The New Democrats finished a solid second, capturing 33 per cent of the vote.

Two years ago, the NDP got just two per cent in the district. And in the 2007 general election, the party didn’t even run a candidate there.

Candidate Jason Spingle says the increase in support sends a big message.

"This has been one of the best-run rural campaigns for our party in the province's history," Spingle said.

"So it's a big establishment, and a lot to build on going forward for the party."

While the Liberals won and the New Democrats gained strength, the governing Tories cratered to third place and a 13.5-per-cent share of the vote.

"I am surprised by the results," PC candidate Dennis Normore acknowledged.

He said he thought it was a "great opportunity" for the district to be on the government side for the next two years.

Premier Kathy Dunderdale is in China on a trade mission, but her office issued a statement in the wake of the results.

"In every election, voters choose who they want to represent them and the people of Cartwright-L’Anse au Clair have exercised that choice today," Dunderdale said.

The premier said she knew the district would present a challenge, given its Liberal history.

"Some difficult decisions were made, and while these decisions were the best ones for the future of the province, we recognize that until people can see the full positive effect of these efforts, people will express their discontent," the premier said.

"Making the right decisions are not often the popular ones. However, having the courage of your convictions and sticking with those decisions for the betterment of your people is the sign of a government with a vision."

Solidly Liberal seat

The district has been solidly Liberal for years.

Jones first won election as an Independent in 1996, after losing the Liberal nomination battle that year. She won as a Liberal in 1999, and later went on to become party leader. Jones served a total of 17 years as MHA before departing for the House of Commons.

The former MHA coasted to victory in the 2011 general election with 71 per cent of the vote.

And even in the blue Tory wave of 2007, when the Liberals won only three seats provincewide, Jones took home a 73-per-cent share of all ballots cast.

Voter turnout was strong in Tuesday’s byelection, coming in at the 70-per-cent mark.