Foxconn Electronics has been actively preparing for production of 4.7- and 5.5-inch new iPhones at its factories in China since July and chairman Terry Guo has been supervising the preparation on the spot to make sure that production lines are in optimal condition, according to industry sources.

In comparison with the iPhone 5, the new iPhones are thinner and therefore are more difficult to assemble, the sources said.

Foxconn has landed orders to initially produce 70% of the 4.7-inch iPhones and 100% of the 5.5-inch models, the sources noted. For the two models, Apple expects total shipments of 70-80 million units by the end of 2014, the sources said.