Will Smith delighted fans with an outdoor concert in London before the British premiere of I, Robot.

Accompanied by DJ Jazzy Jeff, Smith performed for about 3,000 people in Leicester Square. The set included latest single, "Switch."

"When you have these kind of events everybody can't get in. I wanted to give the people who came to support me a little treat out here," the actor-rapper said.

I, Robot, a sci-fi thriller in which Smith plays a detective investigating androids run amok, allowed him to blend long-standing interests, he said.

"From 5 years old I wanted to be a scientist. When I got to 11 or 12 years old I got interested in entertainment. So being in a sci-fi film is a perfect blend of the two," Smith said.