Apple has blamed "external" factors for causing a number of the recent generations of iPhones to explode or catch fire in China and insisted that its handsets posed no safety problem.
A Chinese consumer watchdog said last Friday it had received eight recent reports of iPhones that spontaneously combusted while being used or charged in the country.
In a statement to the AFP news agency late on Tuesday, the US-based tech giant said it had retrieved units for analysis and conducted thorough tests on phones which had experienced "thermal events", but brushed off safety concerns.
"The units we've analysed so far have clearly shown that external physical damage happened to them which led to the thermal event," the statement said.
"We treat safety as a top priority and have found no cause for concern with these products."
The company also denied being slow to respond, after the state-run Shanghai Consumer Council had urged it to address consumer complaints.
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The watchdog's report quoted one woman as saying her iPhone 6s Plus exploded in August, shattering the screen and leaving the battery and back of the phone blackened.
The council said it had received a six-fold surge in total complaints against Apple in the past two months, including sudden shutdowns of the iPhone 6 and 6s even though batteries still had enough power.
The council did not say where the complaining iPhone users were located.
Apple last month offered to change iPhone 6s batteries for Chinese users who complained of the sudden shutdowns, but said the problem did not constitute a safety issue.
Domestic handset makers have received a boost after Samsung in South Korea South recalled 2.5 million Note 7 handsets globally following a series of battery fires, raising distrust of foreign smartphone brands, according to users, analysts and consumer groups.
The Shanghai Consumer Council in its report said that during Samsung's recall in October-November, complaints involving Apple products jumped, accounting for almost half the year-to-date total of 2,763 - itself a nearly two-fold increase from 2015.