A US news reporter was left red-faced when she unwittingly drew a cartoon penis live on TV. Michigan-based Siobhan Riley was reporting for ABC12, when she made the gaffe.

While explaining a traffic holdup in the centre of the city of Saginaw, Michigan, on an interactive street map, Riley set about drawing a diagram to illustrate the problem.

Highlighting where the traffic was congested with lines and circles Riley priduced a distinctly phallic shape. A short clip of the blooper was posted on YouTube and went viral among teenagers of all ages.

"This makes me lol. It's not mature, I'm aware, I'm ok with it," one viewer said.

Another wrote: " Well, you know what was on her mind."

"Oh, Siobhan Riley, thank you for the much-needed belly laugh", a third viewer added.

Riley and ABC12 have not commented.