A California movie screening of a documentary focused on free speech was interrupted by two masked men who forced scared moviegoers to flee the cinema.

Fox News reports that the incident happened at a 1.10pm showing of No Safe Spaces at a Regal Cinema movie theater on Friday in La Habra.

Witnesses say two unidentified men entered the theater wearing bandanas on their faces.

Two masked men intimidated moviegoers at a Regal Cinema in La Habra, California, when they entered an afternoon showing of No Safe Spaces

Filmmakers Adam Carolla (left) and Dennis Prager (right) made the documentary, No Safe Spaces, to discuss free speech in America's current political climate

Vanessa, who declined to give her full name, said: 'After all of the previews and ads were over and the movie was just starting, two thugs sporting hoodies, masks, sunglasses and carrying huge duffel bags ran, not walked, up the aisle and sat at the back of the theater right behind us.'

'They looked like bank robbers, home invasion criminals… they were trying to act scary. As you can imagine, I was nervous that they were planning something even more nefarious than just visual intimidation,' she said.

Moviegoers responded by alerting theater staff and calling the La Habra Police Department, but Vanessa says she still left the movie theater.

She said: 'When the manager went in to check on them they had removed all intimidating items. They knew what they were doing.'

Vanessa said 'potential criminals' were allowed to stay in the theater while others were forced to leave out of fear.

'My son did not want to leave because he didn't want them to succeed in their plan of intimidation and free speech suppression. But I told him a movie was not worth our lives in case they had weapons or something,' she said.

She was issued a refund for her movie tickets.

Scott Stroud, another attendee, said he urged theater management to call police and they complied after initially downplaying the situation by saying the men's backpacks were previously searched.

Stroud explained the movie's subject matter in an effort to convince staff to take his suggestions more seriously.

The La Habra Police Department did not file a police report of the incident and informed Stroud that management did not believe there was a reason for further investigation.

'Common sense says you would want to question them,' Stroud, who disagreed, said.

No Safe Spaces filmmakers Adam Carolla and Dennis Prager said the incident is proof to why the movie is important.

'This story is quite angering, and an example of what is happening increasingly in America. I urge Americans to be courageous. It took courage for us to make this movie and now, apparently, it's going to take courage for Americans to watch it,' Prager said.

'America is the safe space in which we are supposed to be free to hear different ideas, including the ideas in this film, without fear of reprisal, and certainly without fear of physical harm,' he continued.

The documentary, which Prager describes as a 'wake-up call' for Americans, is centered around free speech in America's current political climate and its censorship in certain groups.

He said: 'If I know anything about my fellow Americans, it is that we are not easily frightened by thugs. I urge America to reject the fear that these incidents are designed to engender; be courageous, and go see our movie in a theater.'

Alfred Hopton, publicist for No Safe Spaces, said the film's crew is asking that officers conduct a full investigation into the matter.

'We were very disappointed to hear that our fans were subjected to this and have asked our partners at Regal to look into the matter. We're also asking the police department for a full investigation,' Hopton said.

'We know that Regal values our fans as much as we do and that they share our view that people should be able to enjoy a movie without feeling that they are in danger of being physically harmed.'