Apple reportedly rejected eight million iPhone units delivered by its chief Chinese manufacturer, Foxconn, triggering speculations that another delay will mar the much-anticipated iPhone 5S and iPhone 6 release dates.

The iPhone 5S and its low-cost edition are originally slated to debut June or July this year but KGI Securities predicted last week that a pushback is not entirely far-off. The latest launch date could come September this year.

The same goes with the rumoured Apple phablet, the 4.8-inch iPhone 6, which analysts said would arrive between late 2013 and February 2014. Now, it is more likely that consumers will get a hold of the big-screen iPhone on June 2014, the same report said.

But with the emergence of a fresh production snag, would Apple re-schedule the global rollout of its flagship smartphone?

It appears that the problem lies with Hon Hai, the Taiwanese operator of Foxconn, which will potentially incur losses of up to $US162 million due to the returned handsets, China Business Journal said in a report.

The amount mentioned covers for the repair costs of the defective iPhones, which Apple had reportedly judged as way-below its product standard.

Except for issuing assurance that the problem is being dealt with, Hon Hai officials have yet to officially comment on the matter. There were no indications, however, from the Taiwan-based firm that the incident will cause a major setback on its iPhone production calendar.

Earlier reports have suggested that Foxconn has already set in motion iPhone's full production activities, showing off signals, like the fresh hiring of hordes of factory personnel, that is in a full-swing mode.

Analysts are closely monitoring Apple's 2013 gadget lineup, offering projections that this year's iPhone iterations could prove crucial for the tech giant following the steep slides on its shares value in the past few months.

By the time the iPhone 5S and the iPhone 6 are released, the handsets will have to contain the gains of its chief Android rivals - HTC's HTC One and Samsung's Galaxy S4 and Galaxy Note 3.