A salvage operation was underway after the 125-ton vessel run by Eland Cruise began to sink at about 2:30 p.m. near the Seongsu Bridge that links the Seongdong and Gangnam districts. 

The fire authorities said they rescued six passengers -- including three American and two Thai tourists -- and another five crewmen 15 minutes after the accident and transported them to medical facilities. They had departed from the Jamsil Quay in southeastern Seoul to cruise west and were returning to the origin from around the Dongho Bridge. 

The exact cause of the incident will be known only after a review, but it appears to be a water leak from the engine room that prompted the power generator to halt, according to news reports.

With a “considerable” part of the stern of the boat submerged, the engineers were draining out the water before hauling the ship back to Jamsil.

“We’re having difficulties towing the cruise ship due to its big size and the frozen river,” a fire official was quoted as telling Yonhap News, adding that the authorities have sent a large tugboat to the scene.

By Shin Hyon-hee (heeshin@heraldcorp.com)