Support for Canada's ruling Conservatives has plunged to its lowest level ever while in government, as a reinvigorated opposition presses them over scandals and a sluggish economy, a poll showed Friday.

Prime Minister Stephen Harper's Tories, after sweeping to power in 2006, have the support of 29.4 percent of committed voters, down nearly two percentage points since the last survey in April, according to the Nanos poll.

The Tories held their own against the main opposition party, the New Democrats, which gained almost two percentage points to reach 25.3 percent.

But they have been unable to derail a sudden rise of the Liberals, ranked third in Parliament in number of seats but which has seen its support surge to 34.2 percent.

Pollster Nik Nanos pointed to an expense scandal, the recent election of a new Liberal leader, Justin Trudeau, and also the malaise in the economy for the Conservatives' weak showing in the mid-June survey of 1,000 Canadian voters.

"Roll those three things up and it provides for a very difficult environment for the Conservatives politically," he told public broadcaster CBC.

The number of undecided voters also nearly doubled during all of this political upheaval to 18.4 percent, noted Nanos who said they are probably disenfranchised or "grumpy former Conservatives."

Over the past months, the Conservatives have faced growing criticism over a Senate spending scandal that turned into a criminal investigation as police reviewed a payment to a delinquent senator by the prime minister's chief of staff, who has since quit.

Canadian Prime Minister Stephen Harper's right-hand man, Nigel Wright, resigned suddenly last month after revealing that he paid Can$90,000 (US$87,700) to Senator Mike Duffy in order to help the lawmaker repay funds he had wrongly claimed as Senate expenses.

After the repayment, Duffy stopped cooperating with an audit, leading to opposition cries of a cover-up and demands for a probe.

Meanwhile, Trudeau, the eldest son of late prime minister Pierre Trudeau, was picked to lead and resurrect a party that held power for most of the last century but was relegated to the margins as the country's number three grouping in the last election.

The survey is considered accurate within 3.5 percentage points. So if the numbers hold until the next election, expected in 2015, young Trudeau and his Liberals could form Canada's next government.