Samsung's smartphone sales slump appears to have hit hardest during the launch of the Galaxy S5.

As Digital Spy reports citing the Wall Street Journal, the company shifted four million more Galaxy S4s than the latest model, leaving it with a huge stock surplus.

12 million S5 units were reportedly sold in the first three months, which was about 40% short of Samsung's target.

While sales are climbing in its biggest market, the US, its performance in China has slowed drastically, with S5 sales 50% down on the S4.

There is also talk of a management shake-up, which could see mobile chief JK Shin hand his role over to BK Yoon, who is in charge of Samsung's television and home appliance businesses.

In October, the firm's latest financial results revealed that net profits in its mobile division declined by 73.9% last quarter, while overall operating profit was down by 60%.

In a bid to overcome the slump, Samsung plans to reform its product portfolio by increasing its investment in mid-range and entry-level phones.