PTTGC staff and personnel from the Marine Corps worked all night to clean the beaches at Phrao and Makham bays of Samet, which were tainted with crude oil that leaked from transmission pipe.
The oil spill has now washed into Ban Phe beach, 20 kilometres from Phrao Bay, and an additional 350 staff will reinforce the cleanup crew as soon as possible.
Rayong governor Vichit Chatphaisit, who earlier announced Phrao Bay as a disaster area and close it for three days, has instructed local authorities and villagers to closely monitor the situation.
The oil slick began Saturday morning when about 50 tonnes (50,000 litres) of crude oil leaked from a pipeline, spilling into the sea off Rayong, some 20 kilometres southeast of the Map Ta Phut industrial estate.
The oil slipped from the booms due to the strong winds and waves, washing up on the shores at Samet island Sunday night.
National Park, Wildlife and Plant Conservation Department ordered temporary closure of Phrao bay.
Chairat Trirattanajarasporn, chairman of the Rayong Tourist Association, said some foreign tourists had cancelled planned trips to Samet island for the coming high season this October.
Damage to the tourism business could not be evaluated at the moment, he said, adding that the Rayong Tourist Association would meet today to seek measures to help ease impact on tourism.