(Adds coast guard statement, changes dateline)

By Jo Yong-hak

TAEAN, South Korea, Dec 8 (Reuters) - South Korean workers using skimmers and containment fences battled on Saturday to clean up the worst oil spill in the country's history, as the slick washed ashore near a nature preserve on the west coast.

Parts of about 17 kms (11 miles) of coastline about 100 km southwest of Seoul have already been blackened by oil, the coast guard said. More of the spill is expected on Sunday to hit the area that has marine farms and oyster beds.

"We are taking all measures to prevent that from happening," said Song Myeong-dal, head of the maritime ministry's Information and Policy Monitoring team.

A 20-km slick has extended from a Hong Kong-registered tanker that began leaking an estimated 10,500 tonnes of crude oil on Friday after a barge carrying a crane punched holes in its hull.

The first batches washed up near a nature preserve in the region famed for its beaches and home to a national park that is an important rest stop for migratory birds.

South Korea has already mobilised oil skimmers, containment fences, 103 ships, 5 helicopters and hundreds of troops to head off what could be one of the country's worst environmental disasters since the end of the 1950-1953 Korean War.

It will send more equipment and personnel to contain the spill on Sunday, the Taean coast guard said in a statement.

More than 1,200 local residents scrubbed rocks and removed washed up oil from the coast on Saturday.

There has been no major impact yet on marine life where the first oil reached shore, according to the coast guard but that batch was only a small part of the entire spill.

The largest slick was spreading in Mallipo Bay, a maritime ministry official said.

Heavy winds and high waves hurt oil containment efforts on Friday but seas were calmer on Saturday.

The leak is about a third of the size of the 1989 Exxon Valdez spill of crude oil onto Alaskan shores, which was the costliest on record.

The clean-up alone from that disaster cost around $2.5 billion while the total costs, including fines and settlement of claims, were an estimated $9.5 billion.

The very large crude carrier (VLCC) Hebei Spirit was about 5 miles outside the port, waiting to unload its cargo of some 260,000 tonnes of crude oil from the Middle East, when it was struck by the barge.

Technical managers of the MT Hebei Spirit said in a statement on Friday the crane aboard the barge punched holes in three of the tanker's tanks. (Reporting by Lee Jin-joo, Writing by Jon Herskovitz; Editing by Sanjeev Miglani)

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