Nine people including two children were killed Sunday when high waves slammed into a breakwater on South Korea's west coast, sweeping anglers and others into the sea, coastguard officials said.

Another 14 people were taken to hospital where five of them were still being treated, said Lee Won-Il, a coastguard official, adding that two of the five are in a critical condition.

Lee said the death toll was updated after another body was found and no one is still believed to be missing.

A nine-year-old boy and his father, and a five-year-old boy and his uncle, were among the dead, Lee told AFP.

The incident happened near Boryeong, 200 kilometres (124 miles) southwest of Seoul, during a long holiday weekend, and visitors to the town were among the casualties.

"The sea water receded like an ebb tide before two-metre-high (seven-foot) waves rushed to the breakwater and rocks to sweep the anglers and tourists into the water," Yonhap news agency quoted one witness as saying.

Another witness, restaurant owner Ko Myung-Rae, told Yonhap: "Suddenly, I heard a thunder-like sound which was followed by screams.

"I saw some children crying and heard them saying, 'Our mum is dead'.

"Looking out to sea, there were people floating in the water. I have done business here for 20 years and have never seen something like this before."

The cause of the high waves was not immediately known. The meteorological office said the weather was not particularly bad at the time.

"The wind might have been a bit strong, as we warned earlier. But there were no reasons for us to issue special warnings against tidal waves today," Bong Ji-A, of the local weather office in Daejeon, told AFP.

"It's a bit strange. So we've sent investigators to the area to look into this case."

Witness Lee Sang-Whan estimated the height of the waves at four to five metres. Lee told YTN TV he heard a loud bang, like a sonic boom from an aircraft, just beforehand.

"Shortly afterwards, sounds like an explosion were heard and at the same time, the wave struck the breakwater and swept away people there."

The defence ministry said it had no reports of military manoeuvres in the area.

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The high waves killed 9 people including 2 children

AFP