A former chief of the South Korean unit of Oxy Reckitt Benckiser was summoned for the second time by Seoul prosecutors on Monday to face questioning over suspicions that the British firm sold humidifier sterilizers that resulted in numerous deaths and illnesses here.

Former chief executive officer (CEO) Shin Hyun-woo appeared before the Seoul Central District Prosecutors' Office in southern Seoul as a suspect in the snowballing case that involves numerous deaths since 2011, including some pregnant women.

"I sincerely apologize to the bereaved families of the victims," the 68-year-old told reporters before entering the office. "I will live the rest of my life repenting and seeking ways to help the bereaved families."

The second summons came a week after the current chief of the South Korean unit Ata Safdar formally apologized and promised compensation to the victims of the toxic humidifier sterilizers.

Shin was first summoned by prosecutors late last month, five years after the government confirmed there was a connection between people who died of lung problems and the chemicals used to clean household humidifiers.

He is considered a key figure in the ongoing investigation as he headed the company between 1991 and 2005. The sterilizers in question began reaching the local market in 2001.

Prosecutors said they will grill Shin over whether he was aware of the health risk of the PHMG used in the products. The chemical is known to have caused severe illness or death in those who inhaled it.

On the same day, a former chief of another toxic humidifier sterilizer maker, Cefu, was summoned by prosecutors.

The humidifier disinfectant case, one of the worst scandals involving chemicals in consumer products, came to light after four pregnant women died of lung problems for unknown reasons in 2011. (Yonhap)