The 25 year-old was driving into a building in Los Angeles in the early hours of the morning when a man approached her car and opened the side door.
According to US website TMZ.com, the unknown man told the Jar of Hearts singer to move over, and when she refused he tried to force his way in and hit her on the head and body several times.
Christina pushed the man off and started honking her vehicle's horn until he ran away.
Police have launched an investigation but have not yet found the suspect.