Inhabitants of the Korean peninsula are cleaning up after one powerful typhoon and preparing for another that could be particularly damaging to North Korea, which is still recovering from earlier floods.

The first storm, typhoon Bolaven, left at least 12 people dead in South Korea, including eight fishermen killed in wrecks off the southern coast. The extent of the damage in North Korea, which was hit late on Tuesday and early on Wednesday, was not completely clear, although state media reported that the storm knocked out power, submerged roads and houses and ruined farmland.

Typhoon Tembin was expected to reach South Korea on Thursday, with its outer bands hitting North Korea later in the day.

Tembin is expected to weaken as it reaches North Korea. Heavy rain, however, often means catastrophe in the north because of poor drainage, deforestation and decrepit infrastructure. The north’s official Korean Central News Agency (KCNA) said some areas of Hwanghae and Kangwon provinces would receive up to 70mm (2.8in) of rain on Thursday and Friday.

Weather officials had warned that Bolaven would be the strongest typhoon to hit the region in several years, but its gusts in other parts of Asia were less powerful than predicted.

KCNA reported that Bolaven tore off a power station’s roof, cut power lines in Kaesong city and damaged more than 8,500 hectares (21,000 acres) of maize fields, hurting the chances of a successful harvest.

The typhoon tore roofs off several public buildings in South Hwanghae province and damaged TV relay facilities in North Hwanghae province, KCNA said.

Many houses and roads were submerged or destroyed and railroads were covered by landslides in South Phyongan, Kangwon and South Hamgyong provinces, KCNA said.

Strong winds and rain lashed Pyongyang, the North Korean capital, on Tuesday, but there was little apparent damage there.

Thousands of young people had been brought to Pyongyang to celebrate the anniversary of the founding of the country’s main youth political organisation. The young delegates toured various places in Pyongyang on Tuesday, state media said, and the country’s leader, Kim Jong-un, visited a military unit on the country’s eastern border with South Korea, despite torrential rain.

In the south, Bolaven temporarily left hundreds of thousands without power, caused flights to be cancelled, left nearly 100 families homeless and damaged farmland. The storm also churned up rough seas, which smashed two Chinese fishing ships into rocks off southern Jeju island, killing eight and leaving seven missing. Coastguard ships were still searching for the missing fishermen after an eighth dead body washed ashore on Wednesday afternoon, the coastguard spokesman Ko Chang-keon said.

The coastguard rescued 12 fishermen from the ships on Tuesday, and six others swam or were washed ashore.

The storm killed at least four other people across South Korea, officials said.

The storms come as North Korea tries to help people with food, shelter, healthcare and clean water after heavy flooding in July, according to a recent United Nations situation report. More than 170 died nationwide, and tens of thousands of homes were destroyed in the floods, according to official North Korean accounts.

Many flood victims still live in tents with limited access to water and other basic facilities, the UN report said, and there is worry about increased malnutrition in coming weeks.

2012 Guardian News and Media Limited