President Obama arrived at University Medical Center to visit with Gabrielle Giffords and other victims of Saturday's shooting.
A crowd of people cheered as the motocade pulled up outside the hospital.
At Davis-Monthan Air Force Base, President Obama was greeted by Gov. Jan Brewer, Mayor Bob Walkup, Sheriff Clarence Dupnik, Congressman Raul Grijalva and Davis-Monthan Commander Col. John Cherrey.
Meanwhile, at the University of Arizona — where President Obama is scheduled to speak tonight — police are shutting down Sixth Street in front of Arizona Stadium.
Campbell Avenue is also being cleared by police around the university. Yellow caution tape and police line the street from in front of University Medical Center north of Elm Street.
Police say the number of people in line waiting to get into McKale Center has surpassed capacity.
The doors to McKale opened at 3:51 p.m. and the crowd is filing in.
Overflow crowds are being redirected to Arizona Stadium to see President Obama's address tonight at 6.
Traffic around the university is extremely congested, officials said.
Police officers on foot and in helicopters are monitoring the growing crowd at the University of Arizona as people arrive in droves for a chance to see President Obama tonight.
Near Davis-Monthan Air Force Base — where the president's plane will land — police are closing streets and restricting traffic.
Hundreds of people at the UA mall are writing tribute messages to not only the victims of Saturday’s shooting, but to the community as well.
The messages are being linked together to form a “chain of expression” that will be displayed during tonight’s memorial.
“I wanted to show solidarity and support with the rest of the Tucson community, for Congresswoman Giffords and all of the other families," said Linda Shaw, a department head in the College of Education, who picked up her two children from school in hopes of seeing President Obama.
Her 14-year-old son Andre’s message on the chain of expression read "stay strong and you will get over this horrible tragedy."
His 12-year-old sister Maria echoed the same sentiment “It’s horrible to think someone would kill innocent people.”
A group of UA students who live in a dorm attached to the stadium was playing cards — and betting nuts — to pass the time. They arrived at 10 a.m.
Jessikah Haselhorst , a graduate student, was handing out “memory ribbons” that she made.
“My way of coping with it is to be in the middle of it,” she said.
Noah Sacks, an Ironwood Ridge High School senior, started waiting in line with six friends at 1 a.m. today. They brought folding chairs, blankets, board games and snacks.
"We really wanted to get a good spot," Sacks said. "I just really hoping to hear him give us some hope ... lead us in the right direction from here."
McKale doors open at 4 p.m. and the event begins at 6 p.m.
In honor of today's event, the destination signs on Sun Tran buses will read "Together We Thrive."