Expo tickets for the month of October are in high demand, with two dates in particular - Oct 1 (China's National Day and China Pavilion Day) and Oct 31 (the date of the closing ceremony) - being the most popular.

"I've tried four of the appointed agencies - China Mobile, China Telecom, Bank of Communications and China Post - but failed to get a single ticket for the closing ceremony," said Yu Wei, of Jiaxing in Zhejing province.

His next attempt was to post a thread on an online forum, asking for an Oct 31 Expo ticket, but he has yet to receive a reply.

According to the official website of Expo 2010 Shanghai, "organizers are to stop selling standard-day and multi-day tickets to control the number of visitors during the event's final two months".

The Expo ticketing center said that only tickets bought at the gate, and tickets sold for 14 specific days (Oct 1 to 7 and Oct 25 to 31), will be available from Sept 1.

China Mobile, China Telecom, Bank of Communications and China Post are the only four agencies entitled to sell tickets for the 14 appointed days, which are priced at 200 yuan each.

"Based on the current statistics, 18 million visitors have purchased Expo tickets but haven't come yet, which puts more pressure on Expo traffic before it closes," said a spokesperson for the China Youth Travel Service in Anhui province, who declined to be named.

"To deal with this situation, the Bureau of Shanghai World Expo Coordination might limit the supply of tickets to tour groups (in nearby cities and provinces) in October," he added.

Travel agencies in Anhui province are not the only ones worrying about the short supply of Expo tickets.

"There is not much quota left to us when it comes to tickets for the appointed days in October, though 'lucky' citizens still have a chance," said Zhao Qi, of China Post in Penglai, Shangdong province.

With October tickets in high demand, visitors are expected to flock back to the Expo after a temporary decrease in visitors during the last week of August due to the typhoon weather and schools starting.

"October will be the highest peak in terms of traffic during the half-year event, with an estimated 600,000 to 700,000 visitors per day," said Tang Yibo, manager of the holiday department at Ctrip, a leading online travel agency in China.

"That is why we are advising people to arrange their visit to the Expo in September to avoid a large flow of traffic," he said.

In addition, tickets for Expo's closing ceremony on Oct 31 are in short supply nationwide.

"There are always tourists who postpone their trip until the last day of Expo," said Bob Roger, of BRC Imagination Arts, who has 30 years of experience building pavilions for world fairs.

"At the beginning of October, people will start to realize 'Oh, the Expo will end soon but I haven't visited yet'. Therefore, the last few weeks of the Expo are always the most crowded," he said.