South Korea's biggest automaker Hyundai Motor reported a 30 percent drop in fourth-quarter profits on Wednesday, hit by lengthy industrial strikes and slumping sales in key emerging markets.

In a statement, Hyundai said it posted 1.07 trillion won (US$918.5 million) in net profits during the October to December period, its 12th consecutive quarter of profit downturn.

"Prolonged production stoppages increased the cost burden while economic difficulties in emerging markets hampered sales," the firm said.

Tens of thousands of workers at the firm's plants in South Korea staged strikes for several weeks from July to October demanding higher wages.

Hyundai Motor shares ended the day down 3.07 percent at 142,000 won in Seoul.

Its full-year net profit stood at 5.7 trillion won, down 12 percent from the previous year.

Hyundai sold around 4.9 million cars last year, 2.1 percent fewer than 2015.

The company warned of more challenges ahead in the global auto market, citing "expanding trade protectionism and intensifying competition", but said it aims to sell 5.1 million vehicles worldwide this year.

The scrapping of US participation in a sweeping trans-Pacific trade pact by President Donald Trump has fuelled concerns in South Korea about the prospect of its own free trade agreement with Washington.

During his campaign, Trump called the agreement a "job killing deal" and vowed to renegotiate unfair trade pacts if he were elected.