NEW YORK (MarketWatch) — Apple Inc. has been selling so many iPhone 6 units it has been forced to delay deliveries. This Friday, the iPhone 6 will launch in the world’s largest consumer market, China, where demand is so high one analyst called it “insatiable.”

But at least one brokerage is ringing a siren, warning of inflated expectations heading into the Asian launch that may make it difficult for Apple AAPL, -3.17% to keep pace.

Deutsche Bank downgraded Apple to hold from buy Friday on a reduced price target of $102.

It said Apple’s shares have already priced in the hype from the iPhone 6 and other new products and don’t have much to move on until early next year when the Apple Watch hits store shelves. It also warned of further supply constraints related to the iPhone 6.

A report from Chinese news site Tencent reported Friday that Apple had received 4 million reservations for the iPhone 6. That’s not to be confused with actual preorders, but it nevertheless is a massive number hinting at the potential in China. To give some perspective, Apple last month said it sold a record 10 million phones in its first weekend across all of its launch markets.

“If Apple sells 10 million in its first weekend world-wide without China, and now China by itself wants 4 million? Hold on to your hats,” said Ramon Llamas, a research manager of smartphones at IDC.

Of course, having too much demand and hype isn’t a bad thing if the company and its long list of suppliers and manufacturers can keep pace with it, which most analysts believe can be done.

“Nobody on [Apple’s supply] chain is saying there’s going to be a shortage,” Llamas said. “Don’t underestimate Apple -- this market is going to keep churning well into and past the holidays.”

Even the bearish Deutsche Bank, while downgrading Apple’s stock, raised its sales and earnings estimates to reflect strong demand. It now expects Apple to generate as much as $182.4 billion this year in sales, a reflection of demand for large screen sizes, a large installed base of older-generation 4S phones that might entice consumers to upgrade, and new partnerships with China Mobile Ltd. 941, -1.04% , China Telecom Corp. CHA, -0.49% and China Unicom Ltd. 762, -3.66% , the country’s three biggest carriers.

“We’ve clearly seen pent-up demand for the new screen sizes so it’s unlikely that the company will be losing sales to Android products due to a temporary shortage,” said Ross Rubin, the principal analyst at tech consulting company Reticle Research.

Cantor Fitzgerald analyst Brian White on Tuesday predicted a new wave of “Apple fever” in Asia.

But perhaps Llamas said it best: “Demand is rising too fast? That’s a great problem to have.”

Shares of Apple were up 0.3% to $99.96 in pre-market trade Monday.