The reality TV star and socialite was at the Hollywood launch party when an unidentified assailant rushed onto the red carpet and threw flour over her at around 8.15pm local time.
LA-based photographer Brian Dowling tweeted: "Working the Kim Kardashian party and someone dumped a bag of flour on her head. Craziness!"
TMZ reports that the Los Angeles Fire Department attended the scene to identify the powder. The attacker has also been arrested by police.
Kardashian returned to the event at the London Hotel in West Hollywood after taking 15 minutes to get cleaned up, telling E! Online: "That probably is the craziest, unexpected... thing that ever happened to me. Like I said to my make-up artist, I wanted more powder, and that's a whole lot of translucent powder right there."
She also joked with a red carpet reporter who was filmed handing her a hat after the incident, telling her: "Where were you ten minutes ago?"
Above: The female attacker is held in a police car after her arrest.
Kardashian's sister Khloe wrote that she was "proud of how Kim handled the situation", adding: "I wish I was with my sister tonight. I bet you that woman wouldn't have dared tried a thing."
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See footage of Kim Kardashian on the red carpet at the True Reflection launch below (Note: Clip contains some strong language):