Robert Downey Jr hits Scarlett Johansson accidentally

London: Hollywood actor Robert Downey Jr has reportedly knocked his `Avengers` co-star Scarlett Johansson while fiddling with the high-tech gadgets in his `Iron Man` costume.

Downey, 46, was wearing his heavy superhero suit while he was waiting to film scenes with his glamorous co-star in their new movie `The Avengers`, Contactmusic reported.

However, he suddenly hit the `wrong` button which controls one of the arms and hit Johansson - who plays Black Widow in the movie - in the face.

"Robert triggered a switch that controls one of his arms - and it suddenly jerked backward and whacked poor Scarlett. Knocked silly, she staggered backward, then lost her balance and fell off the low platform they were standing on," a source said.

Stunned crew members rushed to help Johansson.

"Robert, who couldn`t help because he literally can`t move in that iron suit, was beside himself - he kept apologizing and saying, Oh, my God, I`m so sorry!` But Scarlett was a good sport and smiled about the incident," the sorce added.