Their overseas sales plunged 13 percent to 524,060 units last month from the previous year's 600,611 units. Domestic sales declined 5.0 percent to 132,675 from 239,617, findings showed.

The carmakers' poor performance in April was mainly due to a low-growth trend in emerging countries and weak demand in China, the world's biggest automobile market by sales volume, the companies said.

In particular, Hyundai and Kia suffered sharp declines in sales in China amid an ongoing row between Seoul and Beijing over the deployment of the Terminal High Altitude Area Defense system. 

China has opposed the THAAD installation in South Korea as it claimed the battery system's powerful X-band radar system could spy on its military. Seoul has maintained the anti-missile system is aimed at countering missile threats from North Korea.

Sales in Hyundai and Kia plunged 12 percent and 13 percent, respectively, compared to a year earlier to 412,588 and 364,225 units, the companies said.

The three other carmakers generally struggled in April due to lack of demand in major markets and new models.

GM Korea's sales decreased 2.8 percent from a year earlier to 49,163 autos last month. SsangYong Motor's plunged 18 percent year-over-year to 11,071 vehicles sold. Renault Samsung's sales numbers rose by 2.1 percent to 22,444 units, the company said.

To offset lower demand from China, Hyundai and Kia plan to launch more market-specific models in emerging markets such as Russia, Brazil and the Middle East.

In the January-April period, the five companies sold a combined 2.65 million autos, down 5.1 percent from 2.79 million units tallied a year earlier. (Yonhap)