An express bus collided with a guardrail and hit a median strip near a toll of an expressway in western Busan, the country's southeastern port city, at about 6:56 a.m. local time (2156 GMT Friday), Xinhua reports.

All the 22 people on the bus, including a driver, were wounded, and four of them were seriously injured.

Two of the seriously injured were found on the opposite lane of the expressway after being thrown out of the bus due to the impact of the accident.

The seriously injured were not in a life-threatening condition.

The police were investigating the exact cause of the accident, in which the driver was not drunk driving.

Traffic was forecast to be heavy across the country during the autumn holiday, when South Koreans visit their hometowns in rural areas to get together with families and relatives.