The lines are back.

Large crowds of customers queued up for hours — if not days — in cities around the world, like New York, Berlin and Sydney for the new iPhone 6 and iPhone 6 Plus. While Apple is expected to have a blockbuster opening weekend for iPhone sales, analysts are split on whether it will set a new record for the company.

Walter Piecyk, an analyst with BTIG, expects Apple to sell 10 million new iPhones during the first three days, beating last year's record of 9 million iPhones sold during the launch weekend and doubling the number it sold in the first weekend two years earlier.

"This year investors are somewhat cautious about how the exclusion of China could impact first weekend sales," Piecyk wrote in a note [registration required] this week. "However, we suspect that first weekend sales have more to do with Apple’s ability to ramp manufacturing than it does the end market demand."

Likewise, Raymond James analyst Tavis McCourt predicted opening weekend sales will top last year's opening weekend sales of 9 million.

Some analysts are even more bullish on iPhone sales. Maynard Um, an analyst with Wells Fargo, predicted earlier this week that Apple would have "low teens million sales for its first weekend."

Earlier this week, Apple announced it sold more than 4 million new iPhones during the first 24 hours of preorders.

On the lower end, Bernstein analyst Toni Sacconaghi cautioned investors that first weekend sales may come in at just 7 million-8 million.

"Although we see the potential for first weekend sales to disappoint vs. expectations that now appear to be as high as 10M+ units, it is important for investors to keep in mind that 'first weekend sales' are principally a function of available supply rather than iPhone demand," Sacconaghi wrote.

The supply issue is a key concern for many analysts and investors. The iPhone 6 Plus in particular is said to be in tight supply as Apple's manufacturing partners struggle to produce enough larger screen displays for the device. Some looking to preorder device were told it would not ship for weeks or even months.

Tim Cook, Apple's CEO, has previously said that he expects the two new larger iPhone models to set off the "mother of all upgrades."

Apple stock was up slightly in early trading Friday.