In just days, preorders of the iPhone 6 Plus were sold out, signaling not only strong demand but also supply constraints. This early in the game, it’s difficult to gauge just how strong demand for the bigger iPhone 6 model is because we don’t know how much of a supply there was to begin with.

Apple Inc. iPhone 6 Plus Supply Constraints Will Be "Severe": Analyst

Cantor Fitzgerald analysts, however, say supply of the iPhone 6 Plus appeared to be low before Apple Inc. (NASDAQ:AAPL) even started preorders for it.

Monitoring iPhone 6 sales

In their report dated Sept. 12, 2014, analysts Brian White and Isabel Zhu note that there were so many people trying to low onto Apple’s online store when the iPhone 6 models went on sale that it kept crashing. In fact, carriers’ websites were also jammed with traffic. They added that the AT&T model of the iPhone 6 changed to between seven and 14 business days for delivery at around 8:50 p.m. Eastern.

The delivery date for the iPhone 6 Plus extended further though, to between 35 and 42 days at 9:30 a.m. Eastern the day preorders began. At 8:50 a.m., the iPhone 6 Plus had been at between 21 and 28 business days for delivery.

Even though the iPhone 6 will not launch in China until later, the Cantor Fitzgerald team expects the iPhone 6 Plus to be “extremely” popular there.  They say supply for the larger model is going to become even more stretched when the phone is released in China.

Weakness in Apple’s supply chain

The analysts say they found weakness within Apple’s supply chain over the last few months through their Apple Barometer. They said the weakness, especially for Hon Hai and other Apple suppliers during July, indicated that the chain was ramping production for the iPhone 6 later than previously.

As a result, they predict some supply constraints for the iPhone 6 but “severe supply constraints” for the iPhone 6 Plus.

An extended product cycle

The Cantor Fitzgerald team also thinks that this new product cycle will be extended “beyond a couple of quarters,” making it a “powerful” cycle. They say the iPhone 6 with two bigger screen sizes, plus the upcoming Apple Watch launch and the ongoing ramp at China Mobile will combine to create a longer than usual product cycle.

They reiterated their Buy rating and $123 per share price target for Apple, noting that shares still trade at only 11.4 times their 2015 calendar year earnings per share estimate, excluding cash. Because of this, they see “attractive upside” to Apple stock.