The White House just released this statement from President Obama:
This morning, in an unspeakable tragedy, a number of Americans were shot in Tuscon, Arizona, at a constituent meeting with Congresswoman Gabrielle Giffords. And while we are continuing to receive information, we know that some have passed away, and that Representative Giffords is gravely wounded.
We do not yet have all the answers. What we do know is that such a senseless and terrible act of violence has no place in a free society. I ask all Americans to join me and Michelle in keeping Representative Giffords, the victims of this tragedy, and their families in our prayers.
Along with the President, we all have Congresswoman Giffords and her family in our prayers.
The hospital where the Congresswoman is in surgery will be hold a press conference shortly. We'll update as necessary.
Update: TPM has confirmed that a federal judge was shot in the incident, as well.
Update: MSNBC is reporting that according to law enforcement sources, the federal judge has been killed.
Update: The suspect has been identified as 22 year-old Jared Laughner. The assassinated judge is Judge John Roll.
Update: Hospital staff where the Congresswoman was taken are briefing now, 10 total patients, one has died, 5 are in critical condition, 5 in operating room. Congresswoman Giffords is in critical condition. The patient who was killed was a 10 year-old child.