Apple has vowed to investigate reports that a 23-year-old flight attendant in China died of electric shock when she was speaking to someone on her iPhone 5 while charging the phone.

Ma Ailun, who worked with the China Southern Airlines, picked up her iPhone 5 to answer a call while it was being charged and got an electric shock that killed her last Thursday, according to the police.

Ma was planning her wedding on August 8, according to the Chinese State News Agency Xinhua.

Following Ma's death, her sister warned people to refrain from using a phone while it is still plugged in. She also demanded an explanation from the California based global tech company, Apple Inc.

"I want to warn everyone else not to make phone calls when your mobile phone is recharging," tweeted Ma's sister on her micro blog account. Her tweet was reposted by more than 3,000 people on Sina Weibo, which is China's micro blog equivalent to twitter.

"(I) hope that Apple can give us an explanation," tweeted Ma's sister, which went viral on the Chinese social media.

The iPhone was bought last December and was still under warranty and was being charged with the original Apple charger, according to the sister.

Mobiles generally have a low output of 3 to 5 volts and it is not enough to kill anyone, say experts. "However, if the charger or the circuit has a problem, such as a broken wire, it can lead to a shock of 220 volts," a senior physics teacher at a Nanjing high school was quoted as saying in a media report, according to Xinhua.

Last April, Apple issued a public apology to its customers in China after the  media attacked the California based tech company for "poor, unfair and insufficient" repair policies of its gadgets in the country.