Hyundai Motor apologised on Wednesday for a deepening bribery scandal and said its chairman's family would donate $US1bn in shares of an affiliate to charity, Reuters reported.

The news agency noted that prosecutors are investigating whether Hyundai operated slush funds and offered cash for political favours via a lobbyist. Three men have so far been arrested as part of the investigation and several Hyundai executives have been barred from travelling abroad.

"We apologise since as Hyundai Motor Group we should show a good example, but we did not fulfil that responsibility and caused the people concern," Hyundai vice chairman Lee Jeon-kap reportedly told a news conference, lining up with other executives to bow deeply in apology.

"Hyundai will cooperate actively with the prosecutors' investigation and humbly accept the outcome," the company said in a statement cited by Reuters.

The report said Hyundai Motor chairman Chung Mong-koo and his son, Chung Eui-sun, will give away their entire 60% stake in affiliate auto shipper Glovis worth 1 trillion won ($1.05 billion).

Prosecutors told the news agency the donation would not alter the course of the investigation.

Reuters added that prosecutors said Chung Eui-sun would be called in for questioning on Thursday as part of the investigation after Hyundai Motor vice chairman Kim Dong-jin was questioned for a second day on Wednesday.