Sales of Apple Inc's new iPhone 5 could be double those of the previous model in its first week on the market, and up to 33 million iPhones may be sold between now and the end of the month as a result of an aggressive launch plan, analysts said.

Many analysts expressed surprise at how quickly Apple planned to roll out the new model around the world, saying this suggested it would be able to keep up with demand for the bigger, faster and slimmer iPhone.

The new model ships on Sept. 21 in the United States, Australia, Canada, France, Germany, Hong Kong, Japan, Singapore and Britain, and will hit 100 countries by the end of the year in the fastest international rollout for an iPhone so far.

"We are positively surprised that this iPhone rollout is Apple's fastest yet," Barclays Capital said in a client note, adding that it had previously thought supply constraints for sensors in the new screens would hold back initial sales.

"Given this pace it would seem Apple is very well positioned for upside in the December quarter."

Analysts raised forecasts for Apple's share price by as much as $125 to between $750 and $820.

Apple shares were up 0.7 percent at $674.74 before the start of regular trading on Thursday.

Apple will continue to win sales with older models, brokerage William Blair & Co added, putting more pressure on Research in Motion Ltd's BlackBerry, other offerings from Nokia Oyj and less-sophisticated smartphones that use Google Inc's Android software.

"The iPhone 4 will be sold for free after subsidies, replacing the 3GS and providing a strong product to compete in the high-growth, low-end smartphone market," William Blair said.

The brokerage raised its sales forecast for all iPhone models by 29 percent to 33 million for the July-September quarter, at the top of forecasts that ranged from about 20 million to about 30 million in brokerage notes seen by Reuters.

Janney Capital Markets said it expected the iPhone 5 to sell 7 million to 10 million units by the end of the month, while RBC Capital Markets said it expected 8 million to 10 million units to be shipped during the same period.

RBC Capital said sales of iPhone 5 this month could result in additional sales of $4 billion to $5 billion for the fourth quarter ending Sept. 30. The brokerage increased its price target for the stock by $50 to $750.

The iPhone 5 sports a 4-inch "retina" screen that displays a sharper image. It can run on high-speed 4G LTE wireless networks and is 20 percent lighter than the previous iPhone 4S.

Robert W. Baird & Co, which also raised its price target on the stock, now expects Apple to sell 24.4 million iPhones in the September quarter, up from its earlier estimate of 21.2 million.

Barclays, which raised its price target for Apple stock to $810 from $750, said Apple would have a "unique holiday season" as it would also benefit from a launch of a smaller iPad and new Mac computers.

Credit Suisse forecast 20 percent growth in high-end smartphone sales next year, with Apple seen grabbing a 47 percent share, topping archrival Samsung with 40 percent.

It picked the two companies to capture just over half of the overall smartphone market, including less-sophisticated models, putting "tremendous pressure" on RIM, HTC Corp, Nokia and the rest of the Android market.