SEOUL, July 17 (Reuters) - South Korean President Yoon Suk Yeol ordered on Monday an all-out effort to handle the devastation caused by days of torrential rain, as the death toll grew to 39 on Monday, including a dozen people found dead in a submerged underpass.

The rains have pummeled the country's central and southern regions since Thursday, as the rainy season starting in late June reaches its peak, with the interior ministry also reporting nine people missing and 34 injured.

Among the casualties, 12 deaths occurred in a tunnel in the central city of Cheongju, where some 16 vehicles, including a bus, were swamped by a flash flood on Saturday after a levee of a nearby river collapsed. Nine others were hurt.

Yoon convened an intra-agency meeting on disaster response and called for authorities to make the utmost effort to rescue victims and vowed support for recovery work, including designating affected areas as special disaster zones.