Visitors look at an Ioniq electric vehicle by Hyundai at the Hyundai Motorstudio showroom in Goyang, South Korea.[Photo/Agencies]

SEOUL - Hyundai Motor, South Korea's biggest automaker, posted a double-digit expansion in operating profit due mainly to a so-called low base effect, a regulatory filing showed Thursday.

Operating profit was 1.1 trillion won ($978 million) in the July-September quarter, up 12.7 percent from a year earlier.

Revenue increased 9.6 percent over the year to 24.2 trillion won in the quarter, but net income tumbled 16.1 percent to 939.2 billion won.

The third-quarter profit growth was a turnaround from a 24 percent drop in the previous quarter, but the rebound was mainly attributable to the low base effect, in which Hyundai logged an unusually low profit in the same quarter of last year on partial strikes and less business days.

Hyundai's global auto sales reached 1,071,496 units in the September quarter, down 1.2 percent from a year earlier.

The net income stayed below 1 trillion won for two straight quarters as demand for Hyundai-manufactured vehicles weakened especially in China.