Taiwan-based manufacturer Pegatron is working on the handset at its factory in Shanghai, Digitimes understands.
The news backs up previous reports from Japan, claiming that Apple has initiated production on a new phone encased in glass and aluminium.
Apple's next generation iPhone is expected to feature a larger 4-inch class Retina display with a 16:9 aspect ratio, an upgrade from the 3.5-inch display and 3:2 aspect ratio of previous models.
Fresh reports emerged today suggesting that Apple will drop the wide dock connector currently used in its mobile devices when it launches the new iPhone in a controversial move that will see a range of current accessories obsolete.
Pegatron has also been tipped to become a secondary manufacturer of Apple's next iPad, offering support to primary source Foxconn.
Apple's sixth generation iPhone is expected to be released in September or October.