Police say a fire alarm forced authorities to briefly clear the sprawling mall beside the Olympic Park.
The alarms sent hundreds of people into the streets amid wailing alarms a day before the opening ceremony of the Summer Games.
Fears of terrorism have been at the center of preparations for the Olympics, and authorities have twice been forced to deploy troops when security arrangements fell short.
Police allowed shoppers to return after a few minutes. Westfield mall authorities said the alarm was triggered in a restaurant area.