The new phone - which was unveiled last week - went on sale first in Australia, where long lines formed for the opening of the California company's Sydney store at 8 a.m. local time (2200 GMT, Thursday).
Apple has booked more than 2 million pre-orders for the device in the first 24 hours, double the first-day sales of the previous iPhone 4S.
But South Korea's Samsung moved to crash the party on the eve of the phone's debut, saying it planned to add the new device to existing patent lawsuits against its U.S. rival.
Samsung and Apple are locked in patent battle in 10 countries and the stakes are high as the two vie for top spot in the booming smartphone market.
Both companies are also raising marketing spending to promote their latest products ahead of the holiday sales quarter.
Long queues
An estimated 600 people queued around the block from the Apple store in central Sydney and customers were limited to buying a maximum of two phones. In a rainy Tokyo, the lines stretched back several blocks.
Guerrilla marketers grabbed the first dozen or so spots in the queue in Sydney, with companies paying staff members to line up for several days in the hope of being photographed and interviewed for being among the first in the world to get their hands on the new devices.
At the head of the queue was Todd Foot, who lined up with colleagues - all wearing clothing branded with their price comparison website logo - for three days. Staff from an online buyer and seller of used Apple products roamed the long lines offering free coffees.
But most of those waiting were aficionados already hooked on Apple's earlier iPhones and best-selling iPad tablet computers.
"I feel like if I leave it at home, I go a bit crazy," James Vohradsky, a 20-year-old student said of his current iPhone. "I have to drive back and get it. I can't do my normal day without it," said Vohradsky, who had queued for 17 hours with his younger sister.
Some analysts expect Apple to sell up to 10 million iPhone 5 models in the remaining days of September and JP Morgan estimates the phone release could provide a $3.2 billion boost to the U.S. economy in the fourth quarter.
In Japan, where the line outside the Tokyo Apple store stretched for several blocks, one of the two carriers selling the iPhone 5 said it was concerned the U.S. company does not have enough production capacity to meet demand.
Softbank president and founder, Masayoshi Son, said demand for the iPhone 5 was greater than the first iPhone. KDDI Corp, the other Japanese carrier offering the iPhone, said that it had already run out of the iPhone 5.
The new phone has a larger, 4-inch screen and is slimmer and far lighter than the previous model. The iPhone 5 supports faster 4G mobile networks and also comes with a number of software updates, including Apple's new in-house maps feature.
Maps miss mark
The new maps feature, however has been criticized by some users for a number of geographical errors, missing information and a lack of features.
Kim Tudo, a student at the University of New South Wales who queued overnight, said he was disappointed the turn-by-turn navigation feature under the iOS 6 mobile operating system behind the new phone is not immediately available in Australia.
Vohradsky said the lack of mobile payment chip was also "a bit of a letdown". Apple did not embed Near Field Communication (NFC) technology used to turn cellphones into mobile wallets into the iPhone 5.
Tudo and Vohradsky were less bothered by Apple's decision to drop the wide dock connector used in the company's gadgets for the best part of a decade in favour of a smaller one, a move that some critics have noted adds to costs for users who will now have to buy an adaptor for speakers or other accessories.
The iPhone is Apple's highest-margin product and accounts for half of its annual revenue. Apple has said it will make initial deliveries of the iPhone 5 on Friday in the United States and most of the major European markets, such as France, Germany and Britain. The phone then goes on sale on September 28 in 22 other countries.
Apple plans to sell the new phone in 100 countries by the end of the year.
Influential reviewer Walt Mossberg labeled it the best smartphone on the market but criticized the mapping application.
The latest iPhone comes as competition in the smartphone market has reached a fever pitch with Apple up against phones that run on Google Inc's Android software. Android has become the most-used mobile operating system in the world, while Samsung has taken the lead in smartphone sales.
Samsung released new ads mocking Apple fans queuing for the new iPhone, showing users favourably comparing the features of Samsung's top-selling Galaxy S3 smartphone.
Copyright Thomson Reuters 2012
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