President Barack Obama, first lady Michelle Obama, and government employees observe a moment of silence on South Lawn of the White House in Washington, Monday to honor those who were killed and injured in the Tucson shooting rampage. Susan Walsh/AP

President Obama and first lady Michelle Obama will visit Tucson to pay tribute to the victims of Saturday's mass shooting.

The president will speak at a memorial event at the University of Arizona on Wednesday night.

The event, titled "Together We Thrive: Tucson and America," starts at 6 p.m. at McKale Center and is free and open to the public. Doors will open at 4 p.m.

The university said attendees should arrive early because a capacity crowd is expected, and there will be increased security.

The start of a new semester of UA classes has been postponed from Wednesday to Thursday, the university said in a news release.

UA President Robert Shelton and state and federal officials also will speak at the event.

The event will include an American Indian blessing, a moment of silence, a poetry reading and a presentation of a chain featuring messages from the public.