The Shanghai World Expo marked its 100th day Sunday, with the first group of visitors arriving as early as 4 a.m.

Some, like Ni Dan from eastern Jiangsu Province, even chose to stay overnight in front of the Expo Park entrance to guarantee obtaining tickets to some of the most popular pavilions.

Ni, 20, and two of his classmates were the first visitors entering the Expo Park Sunday.

Ni said, "We chose to visit Expo today for three reasons: it's the Expo's 100th day; it's the second anniversary of the Beijing Olympic Games; plus it's the eighth day of the eighth month, which is considered by many an auspicious number."

Sitting on the ground or on 10-yuan (about 1.5 U.S. dollars) plastic folding stools newly purchased from vendors, people chatted, played cards or meditated to reserve energy for a very long day of waiting, walking, viewing and waiting again.

Nearly 38 million visitors, about 95 percent of whom are Chinese and nearly 80 percent are non-Shanghainese, have come to the Expo Park since its opening on May 1, and an average of about 450,000 visitors came to the Expo Park per day in August, equal to the population of a mid-level Chinese county, according to the Expo bureau.

The bureau also said shuttle buses in the Expo park have carried nearly 100 million visitors since the Park's opening, as the buses were out on a run every 14 seconds.

The sudden influx of people has challenged the city's level of openness and hospitality, similar to what Beijing faced during the Olympics two years ago.

Hu Xinyu, a 22-year-old local resident who was back home this year from studying overseas, said Shanghai was greatly changed by the mega event. Hu was surprised to find that many taxi drivers could speak English and volunteers both in and outside the Expo Park were always ready to help.

During the 184 days of the Expo, the number of volunteers will reach about 680,000, including those from 24 foreign countries. This greatly exceeds the 76,000 volunteers assisting during the Beijing Olympics. Most Expo volunteers are from the post-1980 and post-1990 generations.

Xu Yuan of Shanghai Normal University is a volunteer who has worked in both the Shanghai Expo and the Beijing Olympic Games in 2008.

Being an experienced volunteer, Xu still found the most difficult part of volunteering is answering questions. Xu was often besieged by a dozen Expo visitors asking a variety of questions.

-- "The French and Spanish Pavilion, which one I should go to?"

-- "How do I get to the Bund?"

-- "How far is it between Monaco and Morocco?"

-- "Is it Indonesia or India?"