Apple has reported pre-orders of 600,000 for the latest version of the iPhone in the first day, wiping out initial iPhone 4 stocks and surpassing demand for the recently launched iPad.
Thousands of online customers will have to wait until at least 14 July for their iPhone 4, three weeks after the official launch.
Apple was forced to put the US, UK and German Apple store into maintenance mode for a while when the sites failed to cope with the demand.
Online ordering systems at US iPhone carrier AT&T crashed several times before the company postponed shipping dates and eventually stopped taking orders.
AT&T said orders were coming in ten times faster than at the launch of iPhone 3GS in 2009.
Analysts said the demand foreshadows big growth for Apple, which is increasingly likely to reach 10m phone shipments per quarter in 2010, according to the Financial Times.
Apple sold 8.75m iPhones in the first quarter of 2010, more than double the figure for the same period in 2009.
Sales of the iPhone 3GS reached one million over the launch weekend in 2009 and 2m iPads were sold in the first two months, but some observers believe iPhone 4 will exceed both these targets.
The 16Gbyte model is available in the UK online from £499 and the 32Gbyte phone is priced from £599, compared with $199 for the 16Gbyte model and $299 for 32Gbyte version in the US.