Story highlights Crews working to clean up oil spill on Thai beach at Koh Samet

Crude spilled on Saturday during transfer of oil from tanker to undersea pipeline

50,000 liters of oil spilled into the water, though some say it could be more

PTT says remaining crude will be "90% clear by Friday or Sunday at the latest"

A picture postcard beach on one of Thailand's most popular tourist islands is now the focus of frantic efforts to staunch a tide of oil sweeping ashore.

Where pleasure seekers would normally relax on pristine white sand, sandwiched between two lush green headlands, now white-coated cleanup crew smeared with crude suck oil from the shallow waters.

Gobbets of oil lie along the beach, a thin sheen covers much of the wet sand and oil-drenched booms lie like giant black snakes along the shoreline.

The sea is a rust red color and the odor of fuel hangs heavy in the air. Not even a brisk onshore wind can keep the smell away.

For the past four days crude has been washing up here and cleanup crews have been dealing with it the best way they can -- pumping it into holding tanks, containing it with booms, even mopping it up with absorbent pads.

Photos: Photos: Oil spill blackens Thai beach Photos: Photos: Oil spill blackens Thai beach Oil spill blackens Thai beach – A major oil spill on Sunday, July 28, coated Ao Phrao beach on the popular tourist island of Koh Samet in northern Thailand. Authorities estimate that around 50,000 liters (13,200 gallons) of crude oil was leaked from an offshore pipeline belonging to PTT Global Chemical, Thailand's largest petrochemical producer, and 5,000 liters (1,320 gallons) have washed onto the white sand beaches of the island. Hide Caption 1 of 11 Photos: Photos: Oil spill blackens Thai beach Photos: Oil spill blackens Thai beach – Workers continue to remove oil from Koh Samet on Thursday, August 1. PTT Global Chemicals says the Thai navy and approximately 300 PTT workers are continuing to clean up the area. Hide Caption 2 of 11 Photos: Photos: Oil spill blackens Thai beach Photos: Oil spill blackens Thai beach – Clean-up crews have been dealing with the oil in numerous ways -- pumping it into holding tanks, containing it with booms, even mopping it up with absorbent pads. Hide Caption 3 of 11 Photos: Photos: Oil spill blackens Thai beach Oil spill blackens Thai beach – Normally pristine white sand is covered in black muck, pictured on Wednesday, July 30. Hide Caption 4 of 11 Photos: Photos: Oil spill blackens Thai beach Oil spill blackens Thai beach – Thai navy personnel work to clean up the oil spill on Ao Phrao beach on July 30. Hide Caption 5 of 11 Photos: Photos: Oil spill blackens Thai beach Oil spill blackens Thai beach – An oil-stained bucket used in clean-up efforts lies on Ao Phrao beach on July 30. Hide Caption 6 of 11 Photos: Photos: Oil spill blackens Thai beach Oil spill blackens Thai beach – Thai navy personnel are splattered with oil as they work to clean up Ao Phrao beach on July 30. Hide Caption 7 of 11 Photos: Photos: Oil spill blackens Thai beach Oil spill blackens Thai beach – Thai navy personnel work at the scene of the oil spill at Ao Phrao on July 30. Hide Caption 8 of 11 Photos: Photos: Oil spill blackens Thai beach Oil spill blackens Thai beach – Thai navy workers move through the sludge on July 30. Hide Caption 9 of 11 Photos: Photos: Oil spill blackens Thai beach Oil spill blackens Thai beach – Blacked water laps onto the beach in front of a resort on the island of Koh Samet on Monday, July 29. Tourists have been evacuated from the popular Thai weekend destination. Hide Caption 10 of 11 Photos: Photos: Oil spill blackens Thai beach Oil spill blackens Thai beach – Boats work to clean up the spill southeast of Bangkok on Saturday, July 27. Hide Caption 11 of 11

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Map: Oil coats beach near Phrao Bay

Ao Prao beach on the island of Koh Samet is the main impact zone of the 50,000 liters of oil (around 13,200 gallons) spilled during a faulty transfer operation between a tanker and a seabed pipeline on Saturday.

About 600 soldiers, volunteers and workers from PTT Global Chemical, the partially state-owned oil giant that has claimed responsibility for the spill, are involved in the cleanup.

A PTT spokesman says that 70% of the oil has been dealt with. The remaining crude will be "90% clear by Friday or Sunday at the latest."

In some ways Thailand has been lucky. There are more than 200 oil installations in the Gulf of Thailand, which co-exist uneasily in an area known as the marine bread basket of the country.

This spill appears to have been contained to one -- more remote -- beach on the island. The more popular resort areas a few kilometers further south say there is little evidence of the spill.

That's not stopping the tourists leaving though.

Resort operators say many have left, fearing their holiday will be ruined.

But this is low season here with occupancy around 30%. The economic damage would have been far worse a few months from now when most tourists visit, many from the capital Bangkok, 230km to the northwest.

Local fisherman say they've caught fewer fish over the last few days, but it's too early to estimate the damage to fish stocks.

There are no signs of affected marine or bird life at Ao Prao.

The focus is now switching to how this happened. A PTT spokesman told CNN that the leak on Saturday happened as a tanker was transferring crude to an undersea pipe. A giant flexible rubber hose used to transport the oil began to leak.

The hose is replaced every two years. This one had been in operation for just one year.

It's being sent to the manufacturer, Goodyear, for further tests.

PTT is also defending accusations that it has underplayed the amount of oil that leaked.

According to academics at two universities, satellite pictures of the spill, and the amount of dispersants used suggests it could have been twice as big -- 100,000 liters or about 26,000 gallons.

PTT says it is "confident" of its own calculations.

The Thai energy ministry has promised the results of an investigation within seven days.

Meanwhile the cleanup continues. It's a race against time. Every day, the pictures of the spill are flashed around the world increases the likelihood that tourists -- so important to this country's economy -- will go elsewhere for their fun in the sun.