South Korea has deployed more than 100 ships and thousands of troops to clean up the worst oil spill in its history, which has blackened beaches, coated birds in tar and cast a foul smell over a nature reserve.

The slick has washed up in an area spanning 17kms of the west coast, about 100km southwest of Seoul, that is home to popular tourist beaches, a national park and oyster beds.

The spill is threatening to become a major environmental disaster.The slick extends about 20km from the Hong Kong-registered tanker that began leaking an estimated 10,500 tons of crude oil after a barge carrying a crane punched holes in its hull while it was anchored, the coast guard said.

It will likely take more than one month to clean up the mess, maritime minister Kang Moo-hyun told reporters.Volunteers and government personnel have been scooping oil with buckets and absorbent cloth, treating birds covered in oil and scrubbing blackened rocks. Large numbers of fish and waterfowl have been killed.Ships deploying containment fences and oil skimmers have been trying to lessen the spill’s impact.

The largest slick was spreading in Mallipo Bay, a maritime ministry official said.“The oil is about 10cm deep at Mallipo beach and we can’t even see the sand underneath. There isn’t even a single seagull nearby.

They must have fled after the spill,” said Lee Hee-yeol, a top village official in the region.The government has declared several coastal counties to be in a disaster situation.

The leak is about a third the size of Alaska’s 1989 Exxon Valdez crude oil spill, the costliest on record.The clean-up alone from that disaster cost around $2.5-billion.

The total costs, including fines and settlement of claims, were an estimated $9.5-billion. Police are questioning officials of Samsung Heavy Industries, which had the crane on the barge, the barge’s crew as well as the tanker’s owner, captain and crew.

The very large crude carrier Hebei Spirit was 5 miles outside port and waiting to unload some 260,000 tons of crude oil from the Middle East when it was struck by the barge.