At least five people have been killed and a dozen people are missing after a typhoon with winds of up to 170km per hour (kmph) struck South Korea's west coast, forcing two Chinese fishing vessels to sink.

Coast guard rescuers pulled 13 surviving Chinese fishermen from the vessels that capsized off the southern shore of the Jeju island, along with five dead, the emergency services said.

Typhoon Bolaven was expected to eventually make landfall in North Korea late on Tuesday, hitting already damaged farmlands as the country struggles to feed its 24 million population.

Emergency authorities and refiners reported little damage from Bolaven as it tracked through the Yellow Sea, dumping heavy rains on the southern island of Jeju and along the Korean peninsula's coastal regions.

China's Meteorological Administration issued warnings of possible flooding in the coming days that could affect corn and soya crops in parts of its three northeastern provinces that produce about 30 per cent of corn output and 40 per cent of soya.

In South Korea, schools were closed for the day in the capital region and in the south, but financial markets,
industrial and energy installations and government services remained in operation as the storm steered off the coast.

Hundreds of international and domestic flights serving South Korea were cancelled, most scheduled to depart or arrive at the main gateways in Incheon and Gimpo, the transport ministry said.

The storm was expected to hit the southern part of North Korea's west coast, near the farming regions surrounding the capital Pyongyang, the South's national weather service said.

The North, which has trouble feeding its people even in years with good harvest, has said heavy rains in July and August inundated farmlands and triggered landslides, killing hundreds and leaving families homeless.

The UN World Food Programme and an alliance of South Korean aid groups have offered to provide food aid.