At least eight people were killed and 14 others injured Sunday after being swept away by a sudden large wave that crashed over a breakwater on South Korea's west coast, the coast guard said.

The wave — believed to have been as high as 16 feet — slammed over the bulwark near Daecheon Beach in Boryeong City, where dozens of people had been fishing and sightseeing, said Lee Won-il, a local Coast Guard officer.

Lee said up to 15 people remained missing. He said the coast guard was struggling to estimate how many more could be missing because witnesses had given different accounts.

The dead included two children aged 9 and 5, and two of the injured were in critical condition, Lee said.

Witnesses described scenes of grief and panic after the wave washed over the breakwater some 120 miles south of Seoul.

"All of sudden, there was a sound of thunder and lightening and then people screaming," Ko Myung-rae, the owner of a restaurant in the area, was quoted as saying by Yonhap news agency.

"As I went out, children were crying, saying 'Our mother died,"' he said. "As I looked at the sea, I saw people floating there."

Nine coast guard boats and one helicopter aided by four fishing vessels and scuba divers were searching for the missing, Lee said.

South Korea's weather agency had forecast there would be strong winds and high waves in the area but did not issue any advisory, Lee said.

The wave was believed to have been caused by regular tidal movements in the Yellow Sea, he said, adding that it had been cloudy and drizzly around 12:40 p.m. (0340 GMT) when the incident happened.