SINGAPORE - Apple has issued a how-to guide for iPhone users facing a glitch after the latest iOS update caused some devices to go into a repetitive reboot.

It also pushed a 11.2 iOS update at around 4.30pm on Saturday (Dec 2).

Earlier on Saturday, iPhone users facing the problem crowded the Apple Store in Orchard Road.

Photos and videos sent by Straits Times reader Aung Win Htut showed employees at the store demonstrating a temporary fix.

Mr Aung, a Singapore Permanent Resident who is from Myanmar, told ST that he woke up around 6am on Saturday and realised that his iPhone 6 plus had downloaded the 11.1.2 software update.

"It automatically shut down, then it turned back on again, shut down again, and turned back off again," said the 42-year-old marine engineer.

He said he looked online but could not find a solution and so headed down to the Apple Store in Orchard Road.

There were more than 50 people there looking for help for the same problem around 1pm, he said.

"The staff at the store told us that the problem is not only in Singapore but the whole world," said Mr Aung.

An employee told him not all users appear to be affected, as he downloaded the update himself and did not experience any issues.

iPhone 8 user Chan Yi Ren, a 26-year-old speech therapist, told ST that she came "all the way down from the east" to fix her phone.

"It was troublesome but my phone is very important to me so I need to fix it," she said. She was told to turn off all her phone notifications, including background notifications, before downloading the new iOS 11.2.

Another iPhone user, 27-year-old accountant Joyce Lim, told ST that she woke up to her phone blacking out and refreshing.

"I came to the store around 10am, but they were still discussing with their engineers on how to solve it," she said. "I came back just now and they told me to download the new iOS, but the wifi is too slow so I will try to go home to update it."

Tech sites report that the bug is date-related and has been reported by users around the globe.

Users said the issue began when the time turned to 12.15am on Dec 2.

Once that time was logged, the iPhone began "respringing" or going through a repetitive soft reboot, 9to5mac.com reported.

The problem affects several iPhone models. Mr Aung said he saw users with iPhone X seeking help for the issue too.

A temporary fix requires users to manually set the day to a day before the problem started.

ST understands that Apple is aware of the issue and is looking into it.

When ST visited the Apple Store at 4pm, there were about 50 people there seeking help for the bug. Customers were speaking to Apple staff in batches of 10 to get their phones fixed.

By 4.30pm, the number of customers approaching Apple over this problem swelled to more than 150.

Apple issued a how-to guide for users facing the glitch on its support page and pushed a 11.2 iOS update around 4.30pm.

On why problems seem to crop up quite often when there are new iOS updates, as well as why the issues affect the iPhones of some users but not all, Ms Kiranjeet Kaur, a senior research manager for client devices at IDC Asia-Pacific, said that it has to do in part with the many models of the handset available now.

"There's a lot going on at Apple, with the number of iPhone models constantly increasing," she said. "Whatever new features the latest model has, Apple has to make sure they work on earlier models too. Trying to push one software to work across so many different types of hardware is definitely a complex issue."

ST has contacted Apple for more information.