TORONTO -- NDP Leader Tom Mulcair promised to boost an old-age benefit Monday, taking his message to two newly New Democrat ridings the party hopes to retain.

An NDP government would raise the guaranteed income supplement by $400 million, Mulcair told a large, boisterous crowd of supporters in downtown Toronto.

He would first consult with "experts and stakeholders" about how to ensure seniors can get the most benefit, but Mulcair said it's not an idea he expects will meet much opposition.

"I don't think it requires a lot of consultation to say that you want to take seniors out of deep poverty," he said.

"We don't accept as inevitable that the people who built this country should be living in poverty and we're going to change that. I don't think that there's a single senior living in poverty who's going to be against our plan to put more money in their pockets."

Mulcair later visited a retirement home in Mississauga, Ont., where residents seemed either thrilled or completely unmoved by his presence.

The NDP wasn't able to say how much more money seniors would see under the plan because it would vary by level of need, but those living under the poverty line would see an increase, he promised.

Mulcair is also proposing to reverse a Conservative initiative to raise the eligibility for old age security from 65 to 67 -- a move he insisted would be financially sustainable, citing an assessment from the former parliamentary budget officer.

The Liberals have made the same promise.

The full costing of Mulcair's plan remains to be seen, but those details will be forthcoming as the campaign progresses, Mulcair said.

He answered questions on how Monday's downturn in stock markets -- the S&P/TSX index closed down more than 400 points, the Dow nearly 600 -- would affect his platform by criticizing Stephen Harper's focus on oil and gas.

"Mr. Harper's having a hard time because he's left Canadians a less balanced and less stable economy because he bet everything on one sector, which is oil and gas -- unfortunately that's become a destabilizing element," he said.

"But we're going to get back to a balanced economy. I want to be a champion for manufacturing and innovation in this country."

Mulcair's morning event in downtown Toronto focused on the ridings of Davenport and Parkdale-High Park, with introductions from MPs Andrew Cash and Peggy Nash -- along with a fiery extended introduction from former Ontario NDP leader Stephen Lewis.

The NDP took those ridings by wide margins from the Liberals in the 2011 election and believes they can hang onto them.

Also Monday, organizers cancelled a proposed leaders' debate on women's issues because neither Harper nor Mulcair would be taking part. Earlier this month, Mulcair made Harper's participation in debates a condition of his own attendance.

The NDP issued a statement through incumbent candidate Megan Leslie saying Mulcair was the first major party leader to agree "in principle" to the debate, organized by a coalition of organizations calling itself Up for Debate.

"Since the other leaders refused for months to agree to a debate, Tom Mulcair has been working with the Up for Debate coalition to find other ways to highlight women's issues through the campaign," the statement said.