Apple has run out of iPhone 5s in the three days since the new product hit the stores. Sales have appeared to be more than just solid, and there are concerns the company may not be able to meet demand fast enough. US consumer electronics giant Apple sold out of its latest smartphone, the iPhone 5, after the devices hit the stores last Friday, the company announced on Monday. The firm said it sold more than five million pieces, prompting analysts to doubt whether the company would be able to produce the new phone fast enough to meet global demand. "We believe that sales could have potentially been much higher if not for supply constraints," Baird Equity Research Analyst William Power told Reuters news agency. Power expected Apple to sell between eight and 10 ten million units in the fiscal fourth quarter ending in September. Global sales offensive Apple said in a statement it had already shipped the majority of pre-orders to customers, but that some would have to wait until October to receive their deliveries. The iPhone5 has widely been considered as one of Apple's most aggressive international rollouts to date. The device will be available in 31 countries by September 28 and in more than 100 by the end of the current year. "Expectations for Apple products are always white hot," said BGC Analyst Colin Gillis. "It's not just enough for them to break records but to smash them." The US giant has been facing stiff competition from smartphones running on Google's Android software, now the world's most-used mobile operating system.