SAN FRANCISCO - Apple announced on Monday that pre-orders of its iPhone 4S have topped 1 million in a single day, surpassing the previous single-day pre-order record of the company's smartphone.

The iPhone 4S pre-orders surpassed 1 million in the first 24 hours and the previous single day pre-order record held by iPhone 4 is 600,000, according to Apple.

"We are blown away with the incredible customer response to iPhone 4S," Philip Schiller, Apple's senior vice president of worldwide product marketing, said in a statement.

"The first day pre-orders for iPhone 4S have been the most for any new product that Apple has ever launched and we are thrilled that customers love iPhone 4S as much as we do," he added.

The iPhone 4S, which looks the same as the iPhone 4 but has major hardware upgrade inside, is available for pre-order last Friday and set to first arrive in stores in the United States this Friday.

So far, iPhone 4, which, according to Apple, has been sold more than the first three generations of iPhones combined, is Apple's best selling iPhone.

The pre-order numbers are good news for Apple as the initial introduction of iPhone 4S last Tuesday has not lived up to the anticipation of some investors and analysts, and spurred a new wave of concerns about whether the company could keep its innovation momentum in the wake of the passing of its co-founder Steve Jobs last Wednesday.