Former astronaut Mark Kelly referred to the shooting during a Senate Judiciary Committee hearing in Washington on gun violence.
"The initial reports indicate there are three people shot in Phoenix, Arizona with multiple shots fired. There's 50 or so police cars on the scene," Kelly said.
Kelly and his wife, former Rep. Gabrielle Giffords, D-Arizona, this month launched Americans for Responsible Solutions, which seeks to raise money to counter the influence of the gun lobby.
Two years ago, Giffords was shot in the head by a gunman in a parking lot in Tucson.