Hundreds of people gathered at Apple's flagship store in London to be among the first to buy an iPad.
Like many others, the Apple store opened at 0800 BST so eager shoppers could buy one.
The gadget went on sale in the UK, Europe, Japan and Australia, following delays caused by high demand in the US.
There are warnings that some customers who pre-ordered the device by post to get it on the launch date may be disappointed due to delivery delays.
But others have told the BBC that their iPad had actually arrived a day early.
Jake Lee, 17, from Essex, was the first inside the Regent Street store after queuing since midday on 27 May. He said he had not slept at all during the night and had been very cold but was sure that it would be worth it.
Mr Lee was originally going to buy the 32GB version but his dad helped him buy the 64GB after realising his son was first in the queue.
Technology reporter Jonathan Fildes who went along to the Apple store said it was besieged with hundreds of people, the police were on hand to keep people in order and every time a new owner of an iPad emerged they won a cheer from the crowd.
He said there was a "carnival" atmosphere outside the store aided by the appearance of the world's tallest married couple, Wilco van-Kleef and Keisha Bolton, who turned up to promote the Guinness World Records iPad app.
Long-standing Apple fan Stephen Fry also turned up to buy a 3G version of the gadget.
Barry Church, one of the first out of the store with his iPad, said: "I've never used one but I had to have one."
Apple delayed the international launch of the iPad, citing strong demand in the US since its launch on 3 April.
Despite the success, some have criticised the iPad saying it was a closed system that limited what people could do with the books, magazines, music and video they enjoy.
The tablet-device is also starting to see competition from other devices such as the Dell Streak and the established Archos media tablets. Similar devices that run Google's Android operating system are also expected to be released late in 2010.
Customers outside the US have been able to place pre-orders for the iPad since 10 May.
While those that placed orders immediately are likely to get them, others may face a longer wait. Apple's estimates for shipping dates are now mid-June.
Stuart Miles of gadget site Pocket Lint warned that only initial demand would be met by the UK's first batch of iPads. "There will be some stock on the shelves. But it's likely that it will only last for tomorrow," he said.
Two versions of the iPad are available and prices start at £429 including VAT. One model only uses wi-fi to connect to the net and the other can use both wi-fi and 3G mobile technology.
In the UK mobile phone providers Vodafone, Orange, O2 and 3 have revealed details of the price plans for the 3G version. This will require a separate micro-Sim card in order to connect to the net. Existing mobile phone Sims will not work in the iPad.
Those wanting a 3G version will have to buy airtime to use the gadget while out and about.
Mr Miles said he had been using his wi-fi-only US iPad for about a month.
"It's an emotional luxury product," he said. "One that you do not need but once you have it you will find ways to use it."
He agreed that many of the things the iPad offers can be done on other gadgets such as phones and laptops.
"Most of the people in the world do not interact with content, they just consume it," he said. "It's a great device for consuming content but not great for creating it."