(CNN) -- An explosion of an apparent land mine that drifted from North Korea killed one fisherman and injured another, police said Sunday.
The injured man is still hospitalized with serious injuries to his arms and hands, Yeoncheon County Police told CNN. Investigators have found 19 wooden box land mines washed up on the riverside so far, police said.
Heavy downpours in North Korea may have washed the land mines ashore, the South Korean state-run Yonhap news agency reported, citing the South Korean Army.
The military is searching all streams that connect with North Korea, Yonhap said, and has issued warnings to people in the area after investigators found "scores" of the mines, designed to go off when opened.
The explosion occurred just before 11:00 p.m. Saturday (10:00 a.m. ET) in a border city 60 kilometers (37 miles) northeast of Seoul.
State media reported Saturday that South Korean investigators had found eight land mines made by North Korea near the border between the two countries.
A fisherman on Jumun Island alerted authorities after stumbling upon a landmine in a wooden box, Yonhap said, citing a spokesman for South Korea's Joint Chiefs of Staff.
Searchers found seven other mines on Jumum and two other islands in the Yellow Sea, as well as three empty wooden boxes, Yonhap said.
It was unclear how the land mines were identified. According to Yonhap, military officials said the mines may have drifted away from North Korea.
Jumun Island is just below the sea border between the two countries, Yonhap said.
CNN's Brian Walker contributed to this report.