South Korea's president vowed Monday to "completely overhaul" the country's approach to extreme weather from climate change, after at least 40 people were killed by recent flooding and landslides during monsoon rains.

Rescue workers waded through thick mud as they drained a flooded underpass in central Cheongju, searching for more victims after vehicles were trapped in the tunnel by flash floods, the interior ministry said, with nine people still missing nationwide.

South Korea is at the peak of its summer monsoon season and days of torrential rain have caused widespread flooding and landslides, with rivers bursting their banks and reservoirs and dams overflowing — and there is more rain forecast this week.