At least nine people have died in a flooded underpass in Osong-eup, Cheongju, North Chungcheong Province, as of Sunday afternoon. Fire authorities are continuing drainage and operations to search for the missing.

At around 8 a.m. Sunday, fire authorities found the body of a woman in her 70s on a bus, as well as the bodies of four others who have yet to be identified. Another body was found near the underpass entrance at around 8:50 a.m.

Two more bodies, reportedly female, were found in the afternoon, as rescue operations were still underway.

The body of a male victim in his 30s was found Saturday, shortly after the tunnel flooded.

The nine bodies were sent to nearby Cheongju Hana General Hospital, but most of their identities are yet to be confirmed as of 6 p.m. Sunday.

A vehicle was found 50 meters away from the underpass entrance, but no passenger was found.

Also as of 6 p.m. Sunday, four vehicles, including a public bus and a truck, have been towed out of the tunnel. Based on survivors' testimony and surveillance camera footage, it was found that there were about 10 passengers on the bus.

The Gungpyeong 2 underpass tunnel became submerged at around 8:40 a.m. Saturday as a nearby riverbank collapsed due to heavy rains. Water flooded into the underpass within minutes, and about 15 vehicles, including a public bus, became trapped in the four-lane tunnel. The exact number of people who were inside the tunnel is still unclear.

The number of casualties is expected to increase, as 11 people were reported missing after the incident. Surveillance camera footage near the road showed more than 10 vehicles moving toward the underpass, but they were not seen leaving the tunnel.

The total length of the Gungpyeong 2 underpass is 685 meters, with a 430-meter-long underground tunnel. The underpass is estimated to be filled with about 60,000 metric tons of water, according to fire authorities. A large pump has worked to drain about 30,000 liters of water per minute since Saturday.

The operation, however, slowed down due to an inflow of muddy water from the nearby Miho River, fire authorities said.

Seo Jung-il, the chief of the Cheongju Seobu Fire Station, said that the drainage operation has been accelerated since Sunday morning, draining about 80,000 liters of water per minute, but stressed that the mud left inside the tunnel is obstructing the operation.

A North Chungcheong Province official also said that the failure of the drainage pumps inside the tunnel had exacerbated the incident. There were four drainage pumps inside the tunnel, which are capable of handling three tons of rainwater per minute, but the distribution line that supplies electricity to the pump broke down due to the sudden inflow of water from the river, the official said to the local media, Sunday.

Fire authorities secured a small vacant space above the flooded area by stacking sandbags around the underpass throughout the night. Four divers launched the first internal search at around 5:55 a.m. on Sunday. About 30 divers were dispatched to the scene and are taking turns to search for missing people, according to fire authorities. Three hundred and ninty-nine personnel and 65 pieces of rescue equipment are also on-site.

Muddy water inside the submerged tunnel hampered the immediate rescue operation Saturday, authorities said.

Lee Seok-sik, head of the Road Management Office in North Chungcheong Province, played down the possibility of any breathing space remaining inside the submerged tunnel or vehicles on Sunday.

"The Gungpyeong 2 underpass has a rectangular box-shaped structure, which means it is unlikely to have any air pockets," he said in a briefing.

The estimated time to complete the drainage and rescue operation has yet to be determined as of 6 p.m. Sunday.