Authorities are trying to contain an oil slick that has already damaged a stretch of coast in Rayong before it reaches the western shore of famous island Koh Samet.
Natural Resources and Environment Minister Varawut Silpa-archa said on Sunday multiple agencies were deploying teams to try to contain the oil slick as it drifted towards Ao Phrao, a small bay on the holiday island's western shore.
"If the oil reached inside this area it could impact the beach and cause heavy damage to the shallow water corals," Mr Varawut said.
Koh Samet is part of the Khao Laem Ya-Koh Samet National Park.
The Disaster Prevention and Mitigation Department said on Sunday half of Mae Rampheung beach in Muang district was still tainted by the oil that leaked from an underwater pipepine.
A thin layer of oil was deposited along six kilometres of the shoreline from the Fisheries Department's Fisheries Research Centre to Khao Laem Ya, it added.
The area forms part of the 12 kilometres-long area of Mae Rampheung that was declared a disaster area by the province on Saturday.
Mr Varawut said the situation at Mae Ramphueng was improving as workers removed the sludge from the beach and the slick from the sea, but the area remained unsafe.
The latest satellite image from the government's Geo-Informatics and Space Technology Development Agency (GISTDA) showed the oil spill has spread to cover a 67 sq km area of the sea.
Most of the oil had formed a thin film rather than a thick oil slick, navy spokesman Vice Admiral Pokkrong Monthatphalin told reporters, citing aerial photographs.
The crude oil leaked from a pipeline operated by Star Petroleum Refining Plc at a point about 20 kilometres southeast of the Map Ta Phut Industrial Estate on Tuesday night. The exact size of the leak remained unclear, but in its latest press release on Sunday, the company said it was estimated at between 20,000 and 50,000 litres -- smaller than the 400,000-litre figure reported earlier.
