Four people, including two Chinese nationals, were killed and six injured after a bridge collapsed at an expressway construction site in South Korea on Tuesday, authorities said.

Local media aired dramatic footage of what appeared to be a section of the bridge collapsing, sending a massive cloud of smoke into the air.

Four people were killed, five were seriously injured and one suffered a minor injury, a statement from the National Fire Agency said.

Of those killed, two were Chinese nationals and two were South Koreans, an interior ministry official told AFP.

The incident occurred at around 9.50am in Anseong, around 65 kilometres south of the South Korean capital.

"All individuals who suffered injuries are currently being treated at hospitals," the National Fire Agency's spokesperson said.

The National Fire Agency initially said it took place in the nearby city of Cheonan but later corrected that claim.

Hyundai Engineering, the main contractor of the construction site, apologised and said it was assisting authorities.

"We sincerely bow our heads in apology to those who lost their precious lives and were injured in the accident at our construction site," it said.

"We are actively cooperating with the relevant authorities to ensure a prompt resolution on-site" and to identify the cause of the accident, the company said.

Acting President Choi Sang-mok issued urgent directives to mobilise all available resources and personnel for the rescue operation. (AFP)