The 95-foot-long (29-metre) Honolulu-based fishing boat Van Loi ran aground early last week. Coast Guard officials believe it gradually leaked the diesel oil since then and they warned beachgoers to avoid the area.

"At this point there are no reports of marine life impacted from the spill so we think most of the fuel escaped from the vessel and wreckage over time," said Honolulu's US Coast Guard spokesman David Santos. But he said there was concern over possible damage to wildlife.

The Hawaii Department of Land and Natural Resources said the coral reef along the affected beach could be the biggest victim of the ship's grounding.

"We're concerned over damage to the coral from the ship's grounding," said spokeswoman Aulani Wilhelm. "Coraline algae serves as a food source for the near shoreecosystem."

Wilhelm added that 30,000 feet (9,144 metres) of fishing line in the area with about 1,000 large hooks could injure swimmers and entrap marine life. A variety of fish live in nearby waters, in addition to eels, green sea turtles and crustaceans.

Rough weather and surf had so far prevented divers from checking potential damage to the reef, she added.

Diesel leaking from the ship left a sheen on seawater and the beach, observers said. Heavy rains and winds impeded efforts to remove the fuel from the boat before it spilled. The ship eventually broke into three pieces.

Also complicating a clean-up was the curiosity of one endangered Hawaiian Monk Seal that reportedly approached the vicinity of the boat. A federal law designed to protect the seal prohibits humans from coming within 100 yards (100 metres) of the mammal.

"We were concerned with not harming it, but they're very curious animals," Santos said, adding the seal stayed far enough from the boat to allow clean up efforts.