South Korea's capital was blanketed on Wednesday by the heaviest snowfall in Seoul during November on record, with bad weather snarling traffic, knocking out power and grounding hundreds of flights as authorities braced for more snow in coming days.

At least two people were reported killed in traffic accidents on highways east of the capital, while falling debris from buildings and construction sites due to strong winds injured some pedestrians in Seoul, media reports said.

Cooler air moving in from the northwest turned rain into snow overnight, leaving 18 cm on the ground by 3 p.m., marking the biggest fall since records started being kept in 1907, the weather agency said.

The Interior Ministry upgraded its disaster response saying up to 5 cm an hour of snow was forecast through Thursday morning, warning the wet snow had a high concentration of moisture, adding to the risk of damage to facilities and property.

More than 200 flights were cancelled or delayed, most of them domestic as airports across the country experienced severe weather conditions, which also included strong wind, and at least 70 ferries serving islands were suspended.

Power was cut for thousands of households in several areas of Seoul and the central region as electricity lines were damaged by falling trees and snow-related causes, news reports said.