BANGKOK, Dec. 4 (Xinhua) -- Royal Thai Navy vessels on Wednesday were seen on Thai TV cleaning up a long stretch of oil slick off the eastern coast of the Gulf.

The vessels were equipped with skimmers, oil booms and dispersant to soak up and prevent a 4 km stretch of oil slick from moving inward into the coast near Chonburi province, east of Thailand.

The Geo-informatics and Space Technology Development Agency (GISTDA) said on its website that the bunker oil slick is estimated at 20,000 liters, leaked from a capsized oil tanker Golden Bridge 2.

GISTDA, a Thai space agency under the Ministry of Science and Technology, said it has been monitoring the oil slick movement using its Sentinel 2A satellite coastal radar system.

Golden Bridge 2 contained about 104,000 liters of bunker oil when it capsized and sank in high seas in the Gulf on Tuesday, said GISTDA.

Meanwhile, the Department of Natural Resources and Environment has expressed concern that the spilt oil may threaten marine life and corals around Sichang Island and mangrove forests along the coasts.

The Thai Navy did not say when the oil slick will be cleaned up.