Apple Inc broke its silence on complaints about bending iPhones, hours after withdrawing a glitch-ridden software update as the company struggles to restore momentum to the rollout of its latest phones.

"With normal use, a bend in iPhone is extremely rare and through our first six days of sale, a total of nine customers have contacted Apple with a bent iPhone 6 Plus," Apple spokeswoman Trudy Muller said in an email.

Apple shares closed down nearly four per cent at $97.87 on Thursday, wiping out nearly $23 billion in market value.

The new phones face criticism over their bendability, dubbed "bendgate." Social media and online forums have been abuzz with comments about how the new phones can bend when placed in back pockets or while wearing skinny jeans.

Apple said its iPhones feature stainless steel and titanium inserts to reinforce high-stress locations and use the strongest glass in the smartphone industry.

The only way an iPhone may have bent is if someone put it in their back pocket and sat on the phone for a very long time, said Laban Roomes, chief executive officer of Goldgenie, which customizes and gold plates iPhones.

Apple was also forced to withdraw a faulty update to its latest operating system after some users of its new phones complained of call service disruptions.

Apple released a new software update late on Thursday to fix the problems, which it said affected fewer than 40,000 devices.

"I do believe this speaks to execution issues at Apple," said JMP Securities analyst Alex Gauna. "At the end of the day I believe this too shall pass, but we are noting with concern that the miscues pile up."

Apple said on Monday it had shipped 10 million units of iPhone 6 and 6 Plus.

Users of the iPhone 6 and 6 Plus also complained about the inability to use the fingerprint-reading Touch ID after updating to iOS 8.0.1.

Some users had complained of "sluggish WiFi and dwindling battery life" after moving to iOS 8, Time magazine reported earlier this week.

On Thursday, Apple issued a step-by-step guide for users to reinstall iOS 8, launched last week, through the latest version of iTunes. The health app will not work for now and will be fixed in the next software update, the company said.

Customers might, however, hope for replacements for their bent iPhones, depending on whether their devices passed an inspection, tech news website the Next Web reported, quoting an Apple support executive.

"It's not game over for Apple, but nor should we give them a pass on this," Gauna said.

Cases of bent iPhones 5 and 5s had been reported in 2013 by Cult of Mac, a website that exclusively covers Apple.

Rival smartphone makers took digs at Apple's problems.

A Samsung Electronics Co advertisement showcased a bending phone against its own product, while BlackBerry CEO John Chen said: "I would challenge you guys to bend our Passport."

Nestle's Kit-Kat chocolate wafer brand tweeted "We don't bend, we break." - Reuters