Guangdong's hamsters are now flying first class. Manufacturers across the border are shipping the wildly popular Zhu Zhu Pets air freight to United States retailers desperate for the fluffy robotic hamsters, which have become this year's hottest Christmas gift for children. Workers at six toy factories in Shenzhen and Guangzhou are working overtime to fill orders. More than 11 million Zhu Zhu Pets have been sold in the US since the fuzzy electronic hamsters were introduced in May, and demand is high for the holidays. Just days ahead of Christmas, factories were still busy shipping orders valued at US$100 million from retailers in the US and Europe. Some buyers even asked that their orders be delivered by air, regardless of the cost, to ensure their store shelves were filled for Christmas shoppers. 'Sales are just insane,' said Russell Hornsby, chief executive officer of Missouri-based toy company Cepia and creator of Zhu Zhu Pets. Given the huge demand and relatively short supply, some retailers such as Wal-Mart and Target are rationing the toys, with sales limited to one per customer a day. Many shops have simply run out of stock. The palm-sized electronic rodents can squeak, chatter and move around on the ground and have their own accessories, such as houses, tunnels, cars and, of course, hamster wheels. 'They appear real to kids,' Hornsby said. 'And at the same time, you don't have to feed or clean them.' The retail price of a Zhu Zhu Pets hamster ranges from US$8 to US$10 (HK$62 to HK$77). But on online shopping sites like eBay, the price has soared to US$30 or more because of the short supply. Michael Chen, a Cepia manager in charge of toy production and shipping on the mainland, said major retailers placed Christmas orders two to three months ago. All the goods were delivered before November 20, following the industry's normal timetable for the holiday season. 'However, the market feedback went far beyond everyone's expectations. They have had to place a second or third batch of orders,' he said. 'Some retailers know they are very likely to lose money delivering the goods by air. Yet they insisted on doing so because they believe shoppers would not visit their stores unless the hamsters are on the shelves.' While Zhu Zhu Pets were launched at the Hong Kong Toys and Games Fair almost a year ago, children in the city will have to wait until early next year to get one. Spurred by the success of Zhu Zhu Pets, Hornsby said it planned to launch another kind of electronic rodent, called Kung Zhu, next year.