Shanghai World Expo organizers are putting a 600,000-a-day limit on visitors for safety reasons. Visitor numbers inside the Expo site will be subject to a three-level alert system. Authorities will beef up supervision if the volume reaches 400,000. They will conduct visitor-flow-limit after more than 500,000 visitors are counted on site. As soon as the volume reaches 600,000, the organizer will call off transport services to the site for the effectiveness of closure of 42 special bus routes for the Expo as well as Metro stations near the site.

Source: Shanghai Daily - 12/04/2010