Nicole Richie. (AP File)

Socialite Nicole Richie has laughed off rumours she is expecting twins with her boyfriend Joel Madden.

Madden and Richie, who welcomed daughter Harlow in January 2008, are preparing to become parents for the second time, announcing the pregnancy last month.

Richie has since been inundated with rumours that she is carrying twins.

But the star has dismissed the talk, telling reporters at a charity event in Los Angeles on Monday that she is not expecting two children - joking that she "already has twins", referring to her partner and his twin brother, Benji.