Samsung Electronics (SSNF) shares fell sharply in Seoul Tuesday after the world's biggest smartphone maker forecast weaker-than-expected fourth quarter profits, citing a slowdown in China demand that triggered a shock sales warning last week from U.S. rival Apple Inc. (AAPL) - Get Report .

Samsung said profits for the three months ending in December would likely come in at around 10.8 trillion Korean won ($9.67 billion), well shy of the market consensus of 13.2 trillion won. Group sales, Samsung said, would likely fall 11% to 59 trillion won when the company provides detailed metrics of its fourth quarter earnings later this month.

"Operating profits sharply decreased due to lackluster demand in the memory division and intensifying competition in the smartphone sector," Samsung said in a rare explanatory statement alongside the earnings forecast. "Memory demand will rebound in the second half with the release of new CPUs and smartphones."

"In the mid and long term, the supply and demand will be in balance as technical barriers and capital intensity will put pressure on the supply side," the statement added. "As more smartphones are expected to have OLED panels, the display business will explore ways to diversify its market."

Samsung shares closed 1.7% lower in Seoul Tuesday, ending the session at 38,100 won each, a move that extends the stock's six-month decline to around 16.44%

Samsung said a "stagnant and fiercely competitive smartphone market" hit sales of its flagship Galaxy handsets, while weaker memory demand thanks to global adjustments in inventories slowed deliveries of both DRAM and NAND semiconductors, the group's biggest revenue and profit segment.

Samsung said the memory market is likely to remain weak over the first half of this year, but sees improving conditions over the final six months of 2019 and data center and smartphone markets revive.

South Korea's other tech giant, LG Electronics, also posted a much weaker-than-expected fourth quarter profit forecast Tuesday, sending shares lower and raising deeper concerns for the health of the consumer electronics sector.

LG, the world's second biggest television set maker, sees December quarter profits of 75.3 billion won, well below the 387 million won estimate, as sales fall 7% to 15.8 trillion won.

LG Electronics shares tumbled 3.6% following the profit forecast statement, which will be further updated later this month, to end the session at 61,900 won per share, extending their six month decline past 20%.

Last week, Apple spooked global markets after its said its current quarter revenue forecasts would miss estimates thanks in part to slowing sales in China.

In a letter to investors published after the close of trading, Apple CEO Tim Cook said revenue for the three months ending in December would come in around $84 billion, notably shy of the Street consensus of around $94 billion and the company's own previous guidance of between $89 billion and $93 billion.

"While we anticipated some challenges in key emerging markets, we did not foresee the magnitude of the economic deceleration, particularly in Greater China," Cook said. "In fact, most of our revenue shortfall to our guidance, and over 100 percent of our year-over-year worldwide revenue decline, occurred in Greater China across iPhone, Mac and iPad."

The Apple chief pinned the weaker iPhone demand in China on several factors, including a slowing economy worsened by "rising trade tensions with the United States." Cook also cited high prices tied to the strength of the U.S. dollar, fewer carrier subsidies and customers taking advantage of reduced battery replacements in the softened demand for new iPhones.