"We will prepare to send emergency aid to North Korea early next week," South Korea's Yonhap news agency quoted Lee Jae-joung as saying. Initial aid shipments will include noodles, drinking water, powdered milk, blankets and medicines, he said.
Hundreds have died in floods caused by the worst torrential rains ever recorded in parts of North Korea, and a significant proportion of the country's cropland has been destroyed.
The United Nations Food and Agricultural Organization (FAO) has estimated that the country has already lost about one-quarter of the crop destroyed in flooding in 1995, when a resulting famine is believed to have killed some 2 million people.
In a sign of the magnitude of the disaster, the normally secretive North Korean regime has been uncharacteristically forthcoming in describing the extent of the damage.
The Korean Central News Agency (KCNA) reported that rains in some areas along the Taedong River were the heaviest in the country's history, and said that about 11 percent of its rice and corn fields had been destroyed at the height of the growing season.
KCNA said that about 200,000-300,000 people were now homeless, although international aid officials believe the number is probably far higher.
The FAO said that if estimates of the damage to farmland bear out, it could translate into a loss of some 450,000 tons of food - a crushing burden for a nation already facing a million ton shortfall in trying to feed its population.
It is the second year in a row when floods have devastated the country. More than 900 people are believed to have died in similar inundations in 2006.