Portsmouth, New Hampshire - Democratic presidential candidate Kamala Harris on Wednesday implored Americans to bring a halt to the "epidemic of gun violence" plaguing the US, after a mass shooting at a Georgia high school left four people dead.

The vice president, speaking at a rally in New Hampshire, also reiterated her call for an assault-weapons ban – a position widely opposed by Republicans – and support for the further tightening of US gun safety laws.

"This is just a senseless tragedy, on top of so many senseless tragedies," Harris said of the shooting at Apalachee High School in Winder, Georgia, the latest spasm of gun violence to impact a country that has already seen hundreds of mass shootings this year.

"And it's just outrageous that every day in our country, in the United States of America, that parents send their children to school worried about whether or not their child will come home alive," she added.

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"We have to end this epidemic of gun violence in our country once and for all. It doesn't have to be this way," Harris, locked in a tight race with Republican former president Donald Trump, told the crowd before she started laying out elements of her economic plan.

Trump, seen by his party as a champion for gun rights, posted on social media that "our hearts are with the victims," and said "these cherished children were taken from us far too soon by a sick and deranged monster."

Harris, a onetime prosecutor and attorney general of California and former US senator, called on Congress to "finally" pass an assault weapons ban, similar to the one current President Joe Biden helped write as a senator and get passed into law in 1994. That ban expired in 2004, and Congress did not renew it.

Harris also called for adopting universal background checks and implementing so-called red flag laws – state protective orders aimed at preventing certain individuals seen as a threat from purchasing or possessing firearms.

"It is a false choice to say you're either in favor of the Second Amendment or you want to take everyone's guns away," Harris said. "I'm in favor of the Second Amendment, and I know we need reasonable gun safety laws in our country."