Arnold Schwarzenegger. (Photo by Chris Pizzello/Invision/AP, File)

Arnold Schwarzenegger has assured fans "not to worry" after he was assaulted on camera while making an appearance at the the fourth annual Arnold Classic Africa Competition in Sandton on Saturday.

The veteran actor and former politician was filming children competing in a skipping contest when a man tried to approach him from behind.

In the video, the attacker was initially diverted by the celebrity's security before double-backing and launching himself at the 71-year-old in a flying kick that sent the star tumbling into the crowd.

The man was then pinned down and escorted away by security following.

Following the assault, Schwarzenegger tweeted that he only realised he was kicked when he saw the video. "Thanks for your concerns, but there is nothing to worry about. I thought I was just jostled by the crowd, which happens a lot. I only realized I was kicked when I saw the video like all of you. I’m just glad the idiot didn’t interrupt my Snapchat," he wrote.

  The Arnold Classic Africa Competition is a complete multi-sport programme involving more than 70 sporting disciplines, exhibitions and championships.