"Customer response to iPhone 6S and iPhone 6S Plus has been extremely positive and preorders this weekend were very strong around the world," the company said in a statement. "We are on pace to beat last year's 10 million unit first-weekend record when the new iPhones go on sale Sept. 25."
According to an iPhone Inventory blog which tracks the back-order status of the various iPhone models, the wait time for the big-screen iPhone 6S Plus in China is running at three to four weeks, and two to three weeks for the 6S, Re/code reported Saturday.
"As many customers noticed, the online demand for iPhone 6S Plus has been exceptionally strong and exceeded our own forecasts for the preorder period," the company also wrote. "We are working to catch up as quickly as we can, and we will have iPhone 6S Plus as well as iPhone 6S units available at Apple retail stores when they open next Friday."
The company's release this year differs somewhat from 2014, when it announced how many units it sold in the first 24 hours of preorders.
Tech analyst Walter Piecyk at BTIG said Monday it's not clear how to compare initial preorders to 2014.
"Last year, it started on a Thursday night at midnight. This year, because of a late Labor Day, is was Friday night," he told CNBC's "Squawk Box" in an interview. "So we don't know what the comp is, whether they have to wait through the end of Monday to find out exactly what the actual number is going to be."
From a feature standpoint, Piecyk said the new Force Touch incorporated in the iPhone might not be enough on its own for users to upgrade: "But from a functionality [standpoint], it's actually great."
The force-sensitive technology 3D Touch allows what Apple calls "peek and pop," a way for users to preview content with a light touch or open it with a heavier touch.
"It is really going to change the way people use the iPhone," Piecyk said. "It's going you save you time, and that's what people really care about."
Meanwhile, FBR Capital Markets senior analyst Daniel Ives said the preorders suggested a strong trajectory for the iPhone 6S and iPhone 6S Plus.
He said he was encouraged by the response in China, where Apple's website showed particularly long wait times for the phones. "It shows that they are off to a white-hot start, with China really being front and center as a main driver of initial demand."
The company's stock has sunk in recent weeks on concerns about how it will fare amid the downturn in the Chinese economy. "Hopefully this can start to turn the negative tide that's been overhanging the stock," Ives said.
During the market turmoil on China concerns and Apple's growth prospects there, CEO Tim Cook sent an email to CNBC's Jim Cramer on Aug. 24, saying, "We have continued to experience strong growth for our business in China through July and August."
"As you know, we don't give midquarter updates and we rarely comment on moves in Apple stock," Cook also wrote at the time. "But I know ... [the] question is on the minds of many investors."
Early indications the new iPhones are also selling well in China bodes well, Piecyk said Monday.
"[But] Cook put his reputation on the line by sending Cramer the email saying that China's fine. If the numbers don't deliver through that's his reputation that's on the line," he contended.
Amit Daryanani, equity analyst at RBC Capital Markets, said Monday his firm believes sales of 12 million units in the first weekend are a "reasonable expectation."
He noted that 60 percent of incremental revenue came from China in the most recent financial reporting period, so Apple likely anticipated strong demand and positioned a lot of inventory for the market.
"The fact that you're sitting at two to four week lead times already in China and across the world is probably a sign that demand is a lot stronger than people were expecting out of it right now," he told CNBC's "Squawk on the Street."
Daryanani said he trusts the data from the widely cited iPhone inventory blog, which uses screen shots of wait times displayed on Apple's website in order to calculate back orders. That methodology has been a reliable proxy of inventory lag and demand in the past, he said.
The real question, he said, is whether the data from China reflect firm purchase orders—meaning customers have submitted their financial information—or merely soft commitments to buy the 6S and 6S Plus when they become available.
"That's a little unclear candidly, and that's probably one thing that everyone needs to figure out," Daryanani said. "But barring that, I think the numbers sound fairly positive for them."
—Reuters contributed to this report.