MAYO, Yukon - Prime Minister Stephen Harper officially signed the paperwork Friday for Ottawa's contribution to a $160 million upgrade to a Yukon hydroelectric project, and dismissed suggestions his northern tour was nothing more than a pre-election gimmick.

The Mayo B hydroelectric project was given the green light earlier this year and was previously announced by the Conservative government three months ago.

Still, an elaborate photo-op was staged Friday involving Harper and Yukon Premier Dennis Fentie, who toured the facility and took a helicopter ride over the mountainous, picturesque Stewart River.

Journalists, who've followed Harper on his five-day northern tour which wrapped up Friday, were flown by a Canadian air force C-130 Hercules into the tiny community of 250 after being kept in the dark about the destination until the night before.

Critics have complained Harper's events in the three territories this week have been nothing more than repackaged announcements and possibly even a dry-run for a fall election.

The tour itinerary did nothing to dispel that impression as Harper mingled with Mayo residents at the community's gravel airstrip, 400 kilometres north of Whitehorse.

The prime minister led school children on a quick tour of the Hercules plane before returning to the territorial capital around midday local time.

Adding to the photo-op atmosphere, Harper didn't speak to reporters until late in the day at the last event of the tour, a speech in Whitehorse.

New Democrat northern critic Dennis Bevington dismissed the tour as "hollow rhetoric."

But Harper denied there was a campaign vibe to the trip and pointed out he's made four similar excursions to the North since becoming prime minister.

"I'll say over and over again: I have not met a single Canadian, a single real person out there who is telling me they think we should be fighting an election right now," Harper said to a smattering of applause.

Elsewhere Friday, NDP Leader Jack Layton joined with Bloc Quebecois Leader Gilles Duceppe in saying they'd been hearing from the public who want to see the Conservatives defeated in the fall.

The prime minister said the "emphasis of all parties in the House of Commons should be working to ensure we're working on the economy in the fall."

Ottawa's contribution toward the two-stage hydro expansion is $70 million -- cash coming from the Conservative government's $1 billion Green Infrastructure Fund.

It is the first such project to get approval under the fund.

Opposition parties have expressed concern the territory may be digging itself a deep financial hole because it will have to come up with matching funds.

But Fentie defended the project, saying it was line with the territory's energy and environmental plan.

There have also been questions raised in the local media about proposals submitted to the premier by a private company in Alberta that was interested in taking a stake in the deal.

Once completed in 2013, the project is expected to reduce the Yukon's greenhouse gas emissions by 50 per cent from current levels.

The territory was expecting to spend as much as $20 million a year on diesel fuel generators to power its electricity stations, dumping as much as 50,000 tonnes of greenhouse gas into the atmosphere.

The prime minister said the project is a perfect example of how Canada has the potential of becoming a clean energy superpower.

"By investing in these upgrades to this hydro plant today, we are creating jobs, protecting the environment and ensuring a more reliable supply of electricity for the Yukon," Harper said in a prepared statement.

The construction project will involve building a new power house downstream from the existing facility, adding an extra six megawatts to the existing grid.

The second phase involves adding new transmission lines to the existing Carmacks-Stewart grid. The expansion will finally join the territory's northern and southern grids -- something that will lead to a more stable system.

Preliminary site work is expected to get underway this year.