Three children were killed in a house fire in Seoul on Wednesday, police and fire fighters said.

The fire occurred on the third floor of a commercial-residential building in Godeok-dong, southeastern Seoul, at around 3 p.m., they said.

The fire was extinguished about 20 minutes later, but three children -- a four-year-old boy, four-year-old girl and seven-year-old girl -- were found with third-degree burns.  

Rescue authorities performed CPR and took them to a nearby hospital where they were pronounced dead.

The authorities said the children were visiting their grandmother's home, but apparently there were no adults present when the fire broke out.

The authorities said an investigation is under way to determine the exact cause of the accident, and that the fire may have been started by an electric heater in the home. (Yonhap)