US customers wishing to buy an iPad 2 through Apple face a wait of four to five weeks, according to the Apple website - up from the three to four weeks quoted on Monday, Apple Insider has noted.

The iPad 2 only went on sale in the US on Friday last week and is estimated to have sold between 500,000 and one million units already, with many stores reporting that they are completely out of stock.

The high level of demand could force Apple to make a difficult choice between seeing waiting times in the US increase further or delaying the international launch of the iPad 2 in order to satisfy demand at home.

The iPad 2 is due to launch in 35 international markets including the UK on 25 March, but Apple has form where international launch delays are concerned - last year, it pushed back the international launch of the iPad due to higher than expected demand in the US.

UK network operators Three, T-Mobile and Orange are all planning to stock the iPad 2 when it launches in the UK, though interestingly all used vague phrasing - "in the coming weeks" in their official statements regarding timing.

Apple iPad 2 review

Apple hasn't mentioned delaying the launch of the iPad 2 in international markets, though did say that "demand for the next generation iPad 2 has been amazing" and that it was "working hard to get iPad 2 into the hands of every customer who wants one as quickly as possible."