It was possible to walk into a store in US cities on Saturday and buy an iPhone 5, but it took some hunting.

Some stores reported having Apple's newest phone available for walk-in customers, though not all versions of it. A random check of about a dozen stores indicated that most were sold out.

A Verizon store in New York City said the 32 and 64 gigabyte models, but not the 16 GB version, were available. A Sprint store in a suburb of St Paul, Minnesota, said all but the most costly 64 GB iPhone 5s were sold out.

"Before we were even scheduled to open, we were pretty much out," said Eric Rayburn, a worker at a Sprint store in Phoenix.

The iPhone 5 went on sale on Friday, igniting intense interest globally. Apple's website said phones bought online would ship in three to four weeks. Verizon's website said they would ship by October 19.

It's hardly uncommon for supply shortages to make it difficult to get new iPhones in the first days after their release. For Apple, the iPhone introduction is the biggest revenue driver of the year.