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Estimated sales ranged from 400,000 to 600,000, compared with 300,000 sales recorded on the first day for the original iPad in 2010.
Once again demand exceeded supply, with many of Apple's 236 stores and other retailers in the US running out of stock within hours of the first day of sales on Friday.
Analysts said that initial sales of the iPad2 are bound to be higher than the original as10,000 retail outlets are taking part in the launch, compared with only 1,300 the first time around.
In New York, the queue of iPad2 customers included people who had travelled from as far afield as Japan and Russia.
Apple fans in the UK and the rest of Europe who are keen to get their hands on the device, which is thinner and faster than its predecessor and has two cameras, will have to wait until 25 March.
Prices for the iPad2 prices within the same range as the original, at between ₤439 and ₤539.