Thousands of unionised workers at South Korea's top automaker Hyundai Motor staged a partial walkout on Wednesday over a festering wage dispute, a union spokesman said.

More than 7,000 workers were expected to take part in the rolling four-hour strike at the firm's main plant in Ulsan, 300 kilometres (190 miles) southeast of Seoul, said spokesman Hwang Ki-Tae.

About 24,000 unionised workers are employed at the plant, Hwang said, adding that a six-hour walkout was scheduled for Thursday and again on Friday.

The labour union and management have had dozens of meetings this year to negotiate a pay increase and benefits but have failed to reach an agreement.   

The union is demanding a 7.84-percent wage hike, guaranteed job security until age 65 and wants 30 percent of the company's net profit put aside for bonus payments.

The latest walkout marks the fourth straight year of industrial action at Hyundai, which, along with its subsidiary Kia Motors, forms the world's fifth-largest automaking group.

Hyundai Motor's second-quarter net profit plunged 23.8 percent from a year earlier to 1.79 trillion won ($1.55 billion), due to a strong won and increased competition at home and abroad in a global economic slowdown.