It has been a month since U.S.-based Apple Company launched its iPhone 4 series in the Chinese mainland market, yet demand shows no sign of abating.

The smart phone's popularity has even given rise to scalpers (grey marketers) looking to make a quick profit. The scalpers lurk outside stores ready to pounce on anyone who walks out without Apple merchandise.

One scalper offered the 16-gigabyte version of the device for 5,400 yuan (795 U.S. dollars) -- a 10-percent mark-up over the official retail price of 4,999 yuan.

"I have been standing in line repeatedly since the first day of the launch. I purchased twenty iPhones in total so far, and made 3,400 yuan out of them," said a scalper surnamed Huang.

To curb such sales, Apple issued a circular on Oct. 8 requiring buyers to order online in advance before buying the iphone. In addition, every customer was required to present an ID card for registration and allowed to order only one unit per day.

An official at Apple, who wished to remain anonymous, however, admitted that scalpers were difficult to control. "It's like train tickets scalpers -they have pre-ordered and paid the money, so how can we refuse them?" he said.

"Given the convenience factor -- you don't have to pre-order online and you don't need to wait in long queues -- I think the higher price is reasonable," said a man surnamed Xu, who bought a 16 G iphone 4 for 5,700 yuan.