North Korean landmine parts apparently churned up by torrential rains have washed up across the border in South Korea, prompting a search for more weapons, the defence ministry said Saturday.

The wooden shells of two North Korean landmines were found Thursday in a cistern near the Hantan River in Cheolwon County, just south of the inter-Korean border, it said.

"They were just empty wooden shells of landmines. They have no explosives and detonators inside. We assume they might have been washed away," a spokesman for the defence ministry told AFP.

Soldiers were searching areas near the Hantan and Namdaecheon rivers for other North Korean mines, the spokesman said.

Banners have been put up and leaflets handed out to warn holidaymakers in the area of the possibility of stray mines and ask them to report anything suspicious to authorities, he added.

North Korean mines have been carried across the border by floods and landslides in the past. Last year, dozens of wood-cased mines washed up in the South after heavy rains, killing one South Korean and injuring another.

A landslide triggered by this week's torrential rains also dislodged mines planted decades ago on Mount Umyeon in southern Seoul to protect a military installation.

Soldiers said they were still looking for about 10 mines there. Most of the 1,000 mines laid at the site were removed between 1999 and 2006, but a few remain unaccounted for.

Heavy rains have pounded the Korean peninsula over the past week, killing at least 59 people and leaving thousands homeless in the South alone.

South Korea's Yonhap news agency quoted an unidentified military source as saying floods had forced the North to downscale a rare intra-services military exercise involving its army, navy and air force in the tense Yellow Sea.

The North initially assembled about 20 navy vessels including landing craft off the western port of Nampo and deployed MiG-21 fighters to Onchon airbase in the same area.

"However, it hurriedly withdrew troops and equipment (from the southern part of North Korea) on Thursday and Friday, apparently in order to help with restoration work," the source said.

North Korea's official Korean Central News Agency said the downpours had caused "great damage to the people's economy".

According to a preliminary tally, in the North 35,700 hectares (88,223 acres) of rice paddies were inundated, while thousands of homes and hundreds of workplaces were destroyed, along with schools and public buildings, KCNA said.

The south and east were the worst-hit regions, where downpours of up to 500 millimetres fell from Tuesday to Thursday, it said.

The impoverished communist state is already suffering from serious food shortages.