Gun violence in America has taken center stage at this year's Sundance Film Festival, where four films focusing on the divisive issue and its impact are making their debut.

The films -- including "Newtown," a harrowing documentary on the aftermath of the 2012 massacre at a school in Connecticut in which 20 children died -- are sure to amplify the debate about gun control in the United States where mass shootings have become commonplace.

They are also being shown against the backdrop of a presidential race in which gun violence is a hot-topic issue.

"I wanted this to be an intimate portrait that would break through desensitisation," Kim Snyder, the director of "Newtown," told a panel discussion at the festival. "My main goal was to try and pierce through what I think is dangerously happening where none of us can take in these repeated incidents."

"Newtown" looks closely at a broken community as it tries to come to terms with a mass shooting that horrified the nation and was considered a watershed moment in the debate about gun violence.

Several parents who lost children in the massacre open their shattered lives to the camera in the film and speak of their determination to push for tougher gun laws to ensure others don't endure their suffering.

"We knew that this story had to be told," Mark Barden, who lost his youngest son Daniel in the massacre, told the audience after the film's premiere at Sundance.

"We felt that it was very important ... for the vast majority of the people who really care to see this window into what this is and how deep it goes," he added.

Another documentary, "Under the Gun," explores the battle between those who favor stricter gun control measures and those who portray the debate as a threat to the fundamental right to bear arms in America.

The film, narrated by veteran US journalist Katie Couric and directed by Stephanie Seochtig, begins with an ominous message -- "Before this film is over, 22 people will be shot, six will die" -- and explores the political power of the National Rifle Association, the pro-gun lobby group in the United States.

- 'At a tipping point' -

It also follows families who have been impacted by gun violence, including former congresswoman Gabrielle Giffords, who survived a gunshot wound to the head in 2011, and the parents of Jessica Ghawi, one of the victims of the 2012 massacre at a movie theatre in Aurora, Colorado.

Couric said she was inspired to make the documentary after the Newtown massacre as she could not understand the "disconnect" between public opinion, which favours stricter gun controls, and the political class.

"After Newtown, everyone thought it was going to be a watershed moment in this conversation and yet nothing happened," she told AFP.

Seochtig said the film shows that the raging debate about gun control in America is not clear-cut -- "you're with us or against us" -- and that there was a grassroots groundswell in favor of tougher gun laws.

"These five percent of gun owners have dominated the conversation up till now," she said. "But I think change is possible, I think we are coming up to a tipping point.

"People are really taking this issue head-on, including gun owners who have not been represented at all by the NRA."

Two other films that deal with gun violence -- "Speaking is Difficult," a short documentary, and "Dark Knight," a movie loosely inspired by the Aurora massacre -- are also premiering at the Sundance festival that runs through January 31

According to the Centers for Disease Control and Prevention (CDC), there are nearly 33,000 gun deaths in America each year, with 297 people shot on average each day.