4:15 PM EST: Federal Judge John Roll was also killed in the shooting.
President Barack Obama is expected to make a public statement in moments about the shooting.
4:00 PM EST: Gabrielle Giffords has made it through surgery and is in critical condition. She was responding to commands after surgery. A doctor at UMC has said he is very optimistic about her recovery.
"She was shot on one side of her head" "It went through her brain," Trauma Director Peter Rhee said in a press conference.
10 patients, 1 dead, 5 in critical condition, 5 in operating room undergoing surgery at University Medical Center alone, others were transported to different hospitals.
The person who died was a 9-year-old child.
3:55 PM EST Press conference at University Medical Center moved to 4 PM EST.
A news conference with law enforcement authorities has been scheduled for 8 PM EST.
3:45 PM EST The shooter was Jason Loughner of Tucson born in 1988. You can view his strange Youtube videos here. The FBI has confirmed there was just one shooter and that he has a criminal past. 18 people have been injured according to the Pima Country Sheriff's department.
3:44 PM EST Ariz. state senator Linda Lopez tells Fox, "We just heard that she is responding to commands. She made it through surgery."
Five people have been confirmed dead including a member of Giffords staff.
2:50 PM EST BREAKING: Congresswoman Gabrielle Giffords is reportedly alive and in surgery according to local station Kold 13.
A live press conference is scheduled for 3:20 EST and can be seen here.
Watch live local news coverage here.
Listen to live local radio coverage here.
2:14 PM EST Democrat Congresswoman Gabrielle Giffords has reportedly died according to NPR, Fox News and CNN.
12 PM EST Democrat Congresswoman Gabrielle Giffords was shot point blank in the head in Tucson, Ariz. at a local Safeway grocery store during "Congress on Your Corner," her first public event of the year. Three other staffers were shot in addition to 12 bystanders, totaling 16 people injured. No deaths have yet been reported. It has not been confirmed whether security or police were monitoring the event.
Four people are now being reported dead. AZCentral is reporting that University Medical Center spokesman Darci Slaten has confirmed four people have died.
Giffords has been transported to University Medical Center and her condition is not known at this time.
Eye witnesses say a gun man ran up the event and started shooting indiscriminately, he was then was tackled by a bystander. The bystander was shot in this effort. The motive for the shooting is not yet known but it has been reported the gunman has been taken into custody. It is now being reported the shooter may have been a teenager.
According KGUN 9 News, medical helicopters are on the scene evacuating those injured to local hospitals.
Giffords tweeted about the event at 11:58 a.m. EST
Giffords was re-elected to her third term in November. "Congress on Your Corner" events are designed to allow constituents to directly interact and express concerns to their representatives.
Details are still sketchy.
Check back for updates.