Police said a man with an assault rifle walked into a St. Louis business and shot at least three people. Their conditions were not immediately known.
The shooting occurred around 6:30 a.m. (1130 GMT) Thursday. Police believed the gunman was still in the building nearly an hour-and-a-half later.
Police did not give the name of the business but said it was a large firm with numerous employees. STLToday.com, the Web site for the St. Louis Post-Dispatch, said the business is ABB Power.
The Post-Dispatch reported that employees ran to the rooftop to escape the gunfire. The Web site said dispatchers described the gunman as wearing a tan coat and carrying a semiautomatic weapon.