A gunman opened fire at Sandy Hook Elementary School in Newtown, killing 20 kindergarten students. Reports suggest the 20-year-old shooter then turned his gun on himself.
As the full extent of the sick massacre unfolded, stars took to Twitter.com and Facebook.com to express their thoughts and feelings.
New mum Hilary Duff and actress/singer Mandy Moore were among the first celebrities to comment and now stars like Mia Farrow and Arnold Schwarzenegger's estranged wife Maria Shriver have added their comments.
Actress Farrow writes, "PrayForNewtown. Gun control is no longer debatable - it's not a 'conversation' - It's a moral mandate." And former newswoman Shriver adds, "My heart is breaking as this story unfolds. Let's start a #circleofprayer for the children and their families. Just yesterday, I wrote about the joy of becoming a mother. Right now so many mothers and fathers are in indescribable pain. Please say a prayer for the victims of the shooting at Sandy Hook Elementary School in Newtown."
Rap mogul Russell Simmons also offered "prayers for the children, families and faculty of Sandy Hook Elementary School and the people of Newtown," and CNN newsman Piers Morgan tweeted, "I can't bear this. It's just beyond comprehension that anyone would do this in an elementary school. Those poor children. Don't just mourn these poor dead children America - get angry and do something to stop these senseless shootings happening."
Deaf actress Marlee Matlin urged fans to "pray for some sense out of this madness," adding, "I am numb as the numbers of the dead - children and adults - keep ticking up." And Melissa Joan Hart asked, "How could someone be so evil as to kill innocent children at school? God Bless and watch over those families and children that witnessed it!"
Meanwhile, reality TV star Khloe Kardashian Odom tweeted from Miami, Florida, where she was celebrating her nephew Mason's third birthday. She wrote: "To harm children who are defenseless is truly disgusting. I'm in disbelief."
And in another wave of tweets and posts about the massacre, Miley Cyrus asked, "Why does this happen? Why do bad things happen to such good people... Especially young ones," and Rihanna added, "God have mercy!!!! No one deserves this! Praying for the families of the victims of the Connecticut shooting!! What a Christmas it will be."
Evan Rachel Wood, Jared Leto, Rashida Jones, Josh Duhamel and country star Blake Shelton also paused to comment on the tragedy. Honey Bee singer and hunting fan Shelton offered one of the only pro-gun statements when he wrote, "The killing of defenseless people and innocent children. I’m sad and sickened. This is why we all should be prepared to defend and guard."
Lindsay Lohan, whose personal woes are mounting, also took a moment to offer her thoughts on the tragedy, writing, "This is absolutely horrifying. Our thoughts and prayers go out to the families in Newton, CT. So unbelievably sad."