Apple said Wednesday it received 600,000 orders for the new iPhone, a single-day record, as its telecom partner AT&T suspended the troubled early ordering process because of the heavy demand.
Apple also apologized for the difficulties experienced by customers on Tuesday who were seeking to pre-order the latest version of the hot-selling touchscreen smartphone.
AT&T, the exclusive carrier for the iPhone in the United States, said pre-order sales for the iPhone 4 were "10-times higher than the first day of pre-ordering for the iPhone 3GS last year."
"Given this unprecedented demand and our current expectations for our iPhone 4 inventory levels when the device is available June 24, we're suspending pre-ordering today in order to fulfill the orders we've already received," it said.
The Apple and AT&T websites were overwhelmed by requests on Tuesday, the first day of pre-ordering for the iPhone 4, with many customers reporting receiving error messages.
Apple said it had received 600,000 pre-orders for the iPhone 4, which goes on sale in Britain, France, Germany, Japan and the United States on June 24, "the largest number of pre-orders Apple has ever taken in a single day."
The Cupertino, California, firm said demand was "far higher than we anticipated, resulting in many order and approval system malfunctions.
"Many customers were turned away or abandoned the process in frustration," Apple said in a statement.
"We apologize to everyone who encountered difficulties, and hope that they will try again or visit an Apple or carrier store once the iPhone 4 is in stock," Apple said.
In Japan, Japanese mobile phone carrier Softbank also faced a deluge of pre-orders for the latest iPhone, with queues snaking around outlets and its online store overwhelmed by demand.
Hundreds queued in Tokyo in soupy humidity and heavy downpours to place their order for the fourth generation of Apple's smartphone.
Softbank president Masayoshi Son posted a message on social networking site Twitter to apologize for the technical problems. "We are receiving reservations for iPhone 4 much larger than the company had expected," he said.
Apple chief executive Steve Jobs unveiled the new iPhone earlier this month. It features video chat, can shoot and edit high-definition quality video and has a crisper resolution screen.
The iPhone 4 costs 199 dollars for the 16 gigabyte model and 299 dollars for the 32GB version.
The smartphone, which comes in black and white versions, will be available in 18 other countries in July and 24 more in August.
Only the black version was available for pre-ordering in the United States on Tuesday, adding to the frustration of some customers.
Apple has sold more than 50 million iPhones since it launched the device in 2007.
Apple shares gained 2.91 percent on Wall Street on Wednesday to close at 267.25 dollars while AT&T shares were down 0.08 percent to 25.52 dollars.