Apple is investigating claims that a woman was electrocuted while making a call on her iPhone 5 as it was recharging.
Flight attendant Ma Ailun, from the Xinjiang region of China, collapsed to the floor and died as she was using the phone, according to her sister.
She urged other users to be careful, tweeting: "I want to warn everyone else not to make phone calls when your mobile phone is recharging."
Apple said: "We are deeply saddened to learn of this tragic incident and offer our condolences to the Ma family.
"We will fully investigate and cooperate with authorities in this matter."
Police said the 23-year-old victim was picking up the phone to answer a call when she died.
They confirmed Ms Ma, who was due to be married next month, was electrocuted but have yet to confirm if her phone was the cause of the accident, the state news agency Xinhua said.
She bought the iPhone in December at an official Apple store and was using the original charger to recharge the phone when the tragedy happened, her sister said.
Mobile phones have a low output of only three to five volts, which is not enough to harm the human body, according to experts.
People will feel an electric shock at about 36 volts.
"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.
