A state of disaster has been declared in the region where beaches and farms dependent on the sea have been badly affected around Taean, 120km southwest of Seoul.
Booms were set up to contain the oil, and skimmers were working to collect and remove slicks from the water surface, the Taean coast guard said on Sunday.
On the beaches, police, troops and volunteers carried buckets of sludge to huge rubber pools from which they scooped black, oil-mixed sand into sacks.
Three of five oil containers on the Hong Kong-registered tanker were holed in the collision, coast guard officials said.
Two had been emptied by Saturday, and the third was pumped dry overnight.
"The crew on the tanker was able to pump crude oil in the third damaged container into an undamaged one overnight," a coast guard official in Taean said.
"The tanker has stopped leaking since early Sunday. They are still mopping up oil, but it's not work to be done in a few days," he said.
Lee Bong-Gil, who heads the Korea Coast Guard's maritime pollution bureau, told Yonhap news agency: "The large size of the spill has made the containment difficult, but there will be no significant expansion of the oil considering the tide, wind and their speeds."
Local county officials reported on Sunday that the oil slick washing onto the beaches in Taean was already 17km long and 10 metres wide.
"The sea farms there are badly affected by the oil spill. No one knows how many years it will take for them to recover from the damage," Park Tae-Soon, a county official in Taean, said.
He said that while there was no official damage report available yet, there were 445 sea farms in the area for oyster, abalone, clam and other seafood.
The oil slick washing onto the beaches in Taean
was 17km long and 10 metres wide [AFP]
Residents near the beaches of Euihangri and Mallipo also reported pungent oil smells.
The tanker was berthed five miles off Mallipo, near waters designated as a national park, when it was struck by the barge.
The barge floated free and slammed into the port side, tearing three holes in the tanker's hull, when a cable linking it to a tug broke in rough seas.
The stretch of coastline is one of Asia's largest wetland areas, providing important habitat for migrating birds.
The Hebei Spirit had been due to sail into the port of Daesan to discharge its cargo when it was holed.