Sales of Apple Inc's new iPhone 5 may be double those of the previous model in its first week on the market, and up to 33 million iPhones may be sold this quarter, brokerage houses forecast on Thursday.

Many 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 a bigger, faster and slimmer iPhone, which goes on sale this Friday.

Several analysts raised forecasts for Apple's share price by as much as $60, to between $750 and $820. The stock closed at$669.79 on Wednesday.

"We are positively surprised that this iPhone rollout is Apple's fastest yet," Barclays Equity Research said in a note to clients.

Apple will continue to win sales with older models, brokerage William Blair & Co added.

"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.

RBC Capital Markets said it expected Apple to ship 8 million to 10 million of the new models by the end of the month.

The brokerage said this could result in additional sales of $4 billion to $5 billion for the period. It increased its price target for the stock by $50 to $750.

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

It ships on September 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.

Barclays noted the rapid rollout as it increased its price target for Apple stock to $810 from $750.

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.