The Korea Forest Service issued its highest landslide warning for all of mainland South Korea on Saturday.
   
The warning comes as heavy rain that has been hammering the southern part of the country is expected to move north to central areas, raising the risk of major landslides across the country which can threaten lives and damage property.

The highest level in the four-tier landslide alert system warns residents in vulnerable areas to be on the alert as the risk is considered "seriuos."

The warning was already issued Friday for 12 cities and provinces including Busan, Daegu, Gwangju, Daejeon and Ulsan.

On Saturday it was extended to four more areas — Seoul, Incheon and Gyeonggi and Gangwon Provinces — bringing the total to 16.

Jeju Island is the only part of the country where the alert hasn't been raised to the highest level, although the second highest level, "attention," is still in place there.

The Forest Service is on high alert and gearing up to respond to possible emergencies.

Director Park Jong-ho asked residents in areas at high risk of landslides to follow broadcast announcements and emergency text messages and take preemptive shelter at a safe location.

The country has been battered by a record monsoon in recent days.