Two women were killed and 17 others injured Sunday in mountain fires that destroyed dozens of houses in South Korea as thousands of firefighters struggled to stop the flames from spreading.

The fire started Saturday evening in a remote part of the southeastern coastal city of Pohang and was put out by Sunday afternoon after killing a 79-year-old woman and injuring 14 people.

The blaze destroyed 58 houses and left about 120 people homeless, firefighters said.

Police said they were investigating a 12-year-old boy who allegedly set fire to a pile of dry leaves near his hill-side home with friends.

A separate bushfire in Gongju, 95 kilometres (57 miles) south of Seoul, killed an old woman on Sunday.

And a mountain fire raged late Saturday in the nearby port city of Ulsan, injuring three people and scorching 23 houses, according to the National Rescue Services.

Fanned by strong winds, the fire in Ulsan was still spreading Sunday despite efforts by more than 4,000 firefighters and government workers to control it.

The extent of the damage was unclear.