Shipments of iPhone devices are expected to continue to decline to around 40 million units in the second quarter of 2016 (or Apple's fiscal third quarter) after shipments dropped 16% on year to 51.19 million units in the first quarter, sources from the iPhone supply chain in Taiwan have estimated.

The downward projection comes as Apple said that it expects revenues for the second quarter to drop another 15-19% to US$41-43 billion compared to US$50.6 billion of the previous quarter.

Apple may not be able to stage a sales rebound until the third quarter when it released its next-generation iPhone, said the sources.

While the planned release of next-generation iPhones may help Apple regain its growth momentum, the smartphone alone will not be sufficient enough for Apple to sustain significant revenue and profit growth due to weakening economic conditions and saturated smartphone market, the sources added.