Apple's new iPhone 5 has become the fastest-selling iPhone ever, with pre-orders topping two million in the first 24 hours.
A majority of pre-ordered phones will be delivered as planned by September 21, but many will not be delivered until October, it said.
Pre-orders "have shattered the previous record held by iPhone 4S, and the customer response to iPhone 5 has been phenomenal," said Philip Schiller, Apple's senior vice president of Worldwide Marketing.
It is not unusual for Apple products to sell out on the first day.
Orders for the previous iPhone, the 4S, the last product the company introduced before the death of co-founder Steve Jobs, surpassed one million in the first 24 hours, beating Apple's previous one-day record of 600,000 sales for the iPhone 4.
Apple's US store, at www.apple.com, today showed pre-orders for the iPhone 5 would take two to three weeks to ship.
AT&T, the second largest US mobile service provider, said it set a sales record with the iPhone 5 over the weekend, making it the fastest-selling iPhone the company has ever offered.
AT&T did not disclose how many iPhones it sold but said the iPhone 5 was still available for pre-order and would go on sale September 21 at AT&T retail stores.
The phone's other carriers, Verizon and Sprint Nextel, also showed similar delays in shipping the phone.
Topeka Capital Markets analyst Brian White said demand was well above expectations.
"Given the much stronger-than-expected iPhone 5 pre-order sales, we expect a meaningful jump in the three-day sales results for the iPhone 5 compared to the over four million iPhone 4S weekend sales last year," he said.
Although more consumers were opting for the pre-order method, White still expects long lines at the end of the week when the phone goes on sale in stores.
Shipping dates for the slimmer, faster smartphone slipped by a week within an hour of the start of pre-orders.
Apple previously said it would start shipping the iPhone 5 by 21 September in the US and most of the major markets of Europe such as France, Germany and the UK.
It goes on sale on 28 September in 22 other countries.
Analysts have forecast that more than 30 million iPhones, including older models, will be sold by the end of September.
Sales of iPhones account for more than half of Apple's revenue.