The biggest shopping mall in Europe, the Westfield mall next to Olympic Park, was briefly evacuated today after a fire alarm went off. Hundreds of people flooded into the street, but shoppers were allowed to return after a few minutes.

Mall officials say the alarm was triggered in a restaurant area.

At some Olympic Park security entrances, there's a noticeable shift today from having military personnel man the security machines to having civilian security guards. A security firm that is responsible for the bulk of Olympic security says it's getting hundreds more workers each day.

Yesterday, British defense officials scrambled a Typhoon fighter jet after a plane lost contact with air traffic controllers. Communications were quickly restored.

Fears of terrorism have been at the center of preparations for the Olympics. A London bartender says "a lot of people are really excited about the Olympics" -- but that there's also a "sense of dread that something will happen."

And Melissa Johnson, a tourist from Los Angeles, says of all the security, "I'm not sure if I feel safer or just more worried." She says, "You definitely feel like something could happen at any time."

NBC will present the opening ceremonies of the London 2012 Olympics Friday July 27 beginning at 7:30 p.m.