Update: According to CNBC the lockdown has been lifted. This video clip also includes an eyewitness description of what happened:

[End of update.]

Reports are just starting to come in on Twitter:

The President is not at the White House (he was apparently off playing golf). However it seems VP Biden was there:

The White House press corps was also there when the shooting took place. Cheryl Bolen is a White House reporter for Bloomberg:

One person has been shot and transported to the hospital:

This brief clip from CBS News gives an idea of where the shooting took place relative to the White House: