US presidential candidate Kamala Harris has vowed to lower the cost of food by going after “price-gouging” companies, the day after Donald Trump posed with tables of groceries.

Harris gave her first major policy speech on Saturday morning (AEST), appealing to the middle class with promises to reduce food and medicine prices, build three million affordable homes and cut taxes.

The Democrat nominee said the key to ensuring America continued to “define the future and lead the world” was to build up the struggling middle class.

“The middle class is one of America’s greatest strengths,” Harris told supporters in North Carolina.

“Building up the middle class will be a defining goal of my presidency because I firmly believe when the middle class is strong, America is strong.”

The first key issue Harris addressed was the current cost of living — such as food, rent and gas — and she pointed the finger at corporations for over-inflating prices.

She said the cost of bread and ground beef had risen 50 per cent since before the pandemic, even though supply chains had improved and companies were making record profits.

Harris vowed that she would go after the “bad actors” with the “first ever federal ban on price-gouging on food” and penalties for companies that broke those laws.

Vice President Kamala Harris speaks in Raleigh, North Carolina, on the cost of living. Photo: Getty

On housing, Harris said she would work in partnership with industry to build three million homes and rentals “that are affordable to the middle class”.

Plus she would enact laws to crack down on anti-competitive behaviour among investors which she said was driving up the cost of housing.

She promised first-home buyers would benefit from a $US25,000 downpayment.

Another pillar was tax. Harris said she would “let you keep more of your hard-earned money” by giving tax cuts to 100 million Americans, compared to Donald Trump who she said was only offering tax cuts to the rich.

“If you want to know who someone cares about, look at who they fight for,” Harris said.

The vice president’s speech came the day after Trump gave a rambling 80-minute press conference flanked by tables stacked with grocery items.

Trump blamed Harris for the inflation that has caused the price of everyday goods to rise during President Joe Biden’s term in office.

“Harris has just declared that tackling inflation will be a day one priority for her,” he said. “But day one for Kamala was three-and-a-half years ago. Where has she been?”

Donald Trump holds a news conference with tables of groceries outside the Trump National Golf Club Bedminster. Photo: Getty

The press conference at his New Jersey golf club quickly became reminiscent of a Trump rally, with the former president levelling many of the same false claims he typically unleashes on the campaign trail and speaking for 45 minutes before taking his first question.

He insulted Harris repeatedly, saying she is “not smart.” When a reporter noted that some Republicans have urged him to focus on policy, rather than personal attacks, he said, “I think I’m entitled to personal attacks.”

“She certainly attacks me personally,” Trump said.

Trump noted that Harris has called him and his running mate JD Vance “weird,” a criticism made viral by Democratic vice presidential candidate Tim Walz.

He also dismissed the suggestion that he alter his approach, telling reporters, “I have to do it my way.”

Harris’ entry into the race has galvanised Democrats, and polls show she has erased the lead Trump had enjoyed over Biden.

The Harris campaign sent out a mock “media advisory” ahead of Trump’s press conference with the headline, “Donald Trump to Ramble Incoherently and Spread Dangerous Lies in Public, but at Different Home,” a reference to his Bedminster estate.

The grocery staples Trump used as props included household brands like Wonder Bread, Oreo cookies, Folgers coffee and Campbell’s soup.

Bread and coffee prices have actually fallen over the past year, according to the Bureau of Labor Statistics’ monthly Consumer Price Index. Food costs more broadly are now experiencing an inflation rate comparable with when Trump was president — between zero and two per cent a year.

Their substantial price rises in 2022 and 2023, however, have pushed them about 20 to 30 per cent above their levels when Trump left office.

-with AAP