Just hours later, a gunman dressed as a police officer opened fire at an island summer camp for teens, killing as many as 84 people, including several youngsters.
Celebrities were quick to react to the news, taking to their blogs on Twitter.com to express their devastation and send sympathies to Norwegian residents.
In a post on her Twitter page, Perry writes, "Let's pray for our Norway friends as we lay our heads down tonight!"
British rockers Coldplay also remarked on the tragedy, tweeting: "Our love goes out to the people of Norway. What a monstrous thing to happen to such a beautiful country and people."
Singer Josh Groban adds, "Watching the horrible news about what happened in my beloved Norway. Such shocking attacks, sending love to everyone there," while Boy George writes, "Today is the saddest day for the people of Norway, I cannot comprehend the crime, my prayers are with you all! Shocking!"
The West Wing star Lowe told fans, "My thoughts and prayers are with the people of Norway today," as fellow actor Danny Masterson shared, "Send your prayers to Oslo Norway everyone. Disgusting act of violence commited (sic) today. Norway is an amazing country."
Punk icon Henry Rollins paid tribute to the spirit of Norway's citizens, writing, "Been to Norway many times. Awful what happened. A very peaceful place and people," and a stunned Patricia Heaton added, "I can't get my head around the massacre in Norway. That one person can cause such senseless destruction. Pray for the parents of these kids."