Twin typhoons are renewing fears of a humanitarian crisis in North Korea, where poor drainage, widespread deforestation and crumbling infrastructure can turn even a routine rainstorm into a catastrophic flood.

Typhoon Bolaven struck the North on Tuesday and Wednesday, submerging houses and roads, ruining thousands of acres of crops and triggering landslides that buried train tracks. A second major storm, Typhoon Tembin, pounded the Korean Peninsula with more rains on Thursday.

The storms come as North Korea is still recovering from earlier floods that killed more than 170 people and destroyed thousands of homes. That in turn followed a springtime drought that was the worst in a century in some areas.

Foreign aid groups contacted on Thursday said they are standing by in Pyongyang, but had not received new requests for help from the North Korean government. They had little information on the extent of damage and were relying on reports from state media. The country's wariness toward the outside world, as well as a primitive rural road system, means aid may be slow arriving, if it is allowed to come at all.

Typhoon Bolaven swept through parts of northeast China from Tuesday evening to Wednesday, flooding cities and delaying flights (China Daily/Reuters)

"These fresh storms, coming just a few weeks after the serious flooding — they do raise concerns because we see parts of the countryside battered again that have already been left in a vulnerable state," said Francis Markus, spokesman for the International Federation of Red Cross and Red Crescent Societies in East Asia.

Tembin's strong winds and hard rain were pounding South Korea on Thursday, as residents of some cities waded through streets flooded with murky, knee-deep water. The national weather agency in Seoul said the storm would move off the peninsula's east coast and that some cities in North Korea would see severe weather conditions.

There were no deaths reported from Tembin; 20 people were dead or missing in South Korea from Bolaven.

North Korea has yet to release casualty details, though heavy rains that might be little more than an inconvenience elsewhere can be calamitous there.

Downpours trigger landslides that barrel down the country's deforested mountains. For years, rural people have felled trees to grow crops and for fuel, leaving the landscape barren and heavily eroded. Rivers overflow, submerging crops, inundating roads and engulfing hamlets.

Risk of malnutrition

Since June, thousands have been left without clean water, electricity and access to food and other supplies. That leads to a risk of water-borne and respiratory diseases and malnutrition, aid workers say.

Because the North annually struggles to produce enough food from its rocky, mountainous landscape to feed its 24 million people, a poorly timed natural disaster can easily tip the country into crisis, like the famine in the 1990s that followed a similar succession of devastating storms.

A North Korean land management official acknowledged that widespread deforestation and a lack of basic infrastructure have made the country vulnerable to the typhoons and storms that batter the peninsula each year.

"It's important for the future of our children to make our country rich and beautiful," Ri Song Il, director of external affairs for the Ministry of Land and Environmental Protection, said in June.

He said a campaign is under way to replenish forests, build highways and construct proper irrigation at the order of North Korea's new leader, Kim Jong Un. He held up a green pamphlet on land management that was the first official document Kim published after taking power from his father.