US Vice-President Kamala Harris, seeking to sharpen her economic message, pledged to usher in new investments in domestic manufacturing across a range of industries if elected to the White House in November.

In a speech in the must-win state of Pennslyvania on Wednesday, Harris cast herself as "a capitalist" with a pragmatic approach to boosting the middle class.

An hour before the speech, her Republican rival Donald Trump touted his own economic agenda - including a 15% made-in-America tax proposal - while visiting North Carolina.

Both candidates are campaigning in battleground states this week on their competing visions for the economy, a key issue that voters say is a top priority in casting a ballot.

In a tacit rebuttal to Republican claims that she supports "communist" policies, Harris described herself as "a capitalist".

"I promise you I will be pragmatic in my approach," she said at an event hosted by The Economic Club of Pittsburgh.

Building on her vision for an "opportunity economy", Harris laid out new proposals to help young families, first time homebuyers and the elderly through $100bn worth in tax breaks and financial incentives. She vowed new investments in artifical intelligence, aerospace and energy development.

Harris added, however, that tax rates for large corporations and the wealthiest Americans must rise so they "pay their fair share".

She also promised to reform permitting to speed up building in the US, eliminate college degree requirements for federal jobs and increase union apprenticeships, if elected.

“I intend to chart a new way forward and grow America’s middle class” she argued, while Trump has “no intention to grow our middle class — he’s only interested in making life better for himself and people like himself”.

Later in her first major solo interview with MSNBC, Harris lambasted Trump, saying he "isn't very serious" on his tariff proposals and "constantly got played by China".

“You don’t just throw around the idea of tariffs across the board," she said. "He’s just not serious about very many of these issues."

Harris also pushed back for the first time on the Trump campaign's claim that she is lying about having worked at McDonald's as a university student.

"Part of the reason I even talk about having worked at McDonald's is because there are people who work at McDonald's in our country who are trying to raise a family," she said. "I worked there as a student."

Harris's remarks came as she is seeking to chip away at Trump's advantage with voters on his handling of the economy.

Though the race remains close, Harris has opened up a narrow lead in national polling since the two candidates met on a debate stage earlier this month.

At a campaign event in Mint Hill, North Carolina, Trump defended his tariff proposals and suggested they were the reason "people in [other] countries want to kill me".

“I’m imposing tariffs on your competition from foreign countries, all these foreign countries that have ripped us off, which stole all of your businesses and all of your jobs years ago,” he said.

He reminded supporters that, as president, he had passed the largest corporate tax cut in US history, from 35% to 21%.

The centrepiece of his second term, he said, would be a "manufacturing renaissance" ushered in by a 15% tax rate for products made in America.

The economy routinely emerges as the top issue for voters this November and both candidates have touted populist policies, with Harris appearing to mirror a Trump proposal to end taxation on service workers' tips.

In her sitdown with MSNBC, Harris said that "Donald Trump has a history of taking care of rich people".

"I'm not mad at anybody for being rich, but they should pay their fair share," she added, arguing that Trump advocates "tax cuts for the billionaires and the top corporations in our country".

"My perspective on the economy is when you grow the middle class, America’s economy is stronger, and there’s empirical evidence to prove my point correct."