Expo tickets have been running out at many authorized ticket outlets both in and out of Shanghai, due to what they call a "tightened supply" from the organizers.

In cities including Guangzhou, Nanjing, Hangzhou and Shanghai, many outlets of the four authorized agents, namely China Mobile, China Telecom, Bank of Communications and China Post, have reported surging sales of Expo tickets but less supplies from the organizers recently.

Staff at the Guangzhou office of China Telecom, for example, said only a few Designated Day Tickets are available, that is, from Oct 1 to 7 and Oct 25 to 31. All the other tickets have sold out. Similarly, in Nanjing, China Telecom has set a maximum limit of 50 standard tickets to be sold in a day due to limited supply.

Even in Shanghai, many convenience stores that have been allowed to sell Expo tickets had no more tickets this past week. Staff at a China Post outlet near the commercial street of Huaihai Road also said they had not received any new supplies of tickets from the organizers in the past week.

Visitors, however, can still buy tickets for the day - meaning they can enter only on the same day the ticket is purchased - at the major entrances to the Expo Garden. Major travel agencies also have not had the same problem of short supply, according to local media reports.

But already the shortage of tickets is causing confusion and complaints. Ding Shijie, a Shanghai resident, said he recently spent half a day running to different authorized ticket outlets in the city's Baoshan district, but only one supermarket was selling the tickets.

"I want to buy the tickets for my friends outside Shanghai, since they complained to me they were difficult to get. But I was surprised that it's the same in Shanghai," he said.

Authorities would not comment on the issue when contacted by China Daily. Xu Wei, spokesman of the Expo Coordination Bureau, only said he has not received recent complaints about the limited supply of Expo tickets.

But a source familiar with the matter told China Daily that the authorities encourage the sale of tickets for the day, because this way, they have an easier time controlling the number of visitors in a single day. Once the headcounts exceed the daily capacity of the Expo Garden, the authorities can call an end to the sale of tickets for the day, he said.

Safety and order have been the top priorities for Expo organizers with the sharp increase of visitors as summer descends. Authorities earlier cancelled a long-anticipated concert by the famous Japanese pop band SWAP on June 13 over safety concerns. The action came after scuffles and arguments occurred when tens of thousands of fans scrambled to get into an earlier concert by South Korean pop music singers.

Despite a lackluster opening period, when an average of 160,000 people visited the first five days of the Expo, its popularity soon escalated with more than 420,000 visitors flocking to the fair on June 1.

Early estimates put the total visits at 70 million, or a daily average of 380,000.

The difficulty in buying tickets at authorized agents recently has prompted many to go online for help. Both e-commerce sites and message board sites have reported booming sales.