The State Oceanic Administration said in a statement late Sunday that three oil slicks with a total surface area of 332 square kilometers had been most recently spotted, up from 101 square kilometers reported on Wednesday, presstv.com reported.
Three coast guard vessels were on the scene assessing the spill, the oceanic administration added.
The Iranian tanker, named Sanchi, was carrying 136,000 tons of light crude oil when it collided with a huge Chinese freighter named the CF Crystal in early January.
Officials cite evidence to conclude that all sailors aboard the ill-fated oil tanker that was burning in Chinese waters for days died early into the collision.
The type of condensate oil carried by the Sanchi does not form a traditional surface slick when spilt, but is nonetheless highly toxic to marine life and much harder to separate from water. The cargo amounted to nearly one million barrels (bbl) of oil.
Media quoted environmental organizations as saying that the site of the sinking is an important spawning ground for species like the swordtip squid and wintering ground for species like the yellow croaker fish and blue crab, among many others.
It is also said to be on the migratory pathway of numerous marine mammals, such as humpback and grey whales.
Earlier reports from Wednesday said an oil slick measuring about 101 square kilometers had been spotted, showing the polluted area had expanded by three times in size.
This handout file picture from the Transport Ministry of China taken on January 14, 2018 shows smoke and flames coming from the burning oil tanker, Sanchi, at sea off the coast of eastern China. (AFP)
China is continuing its cleanup operations in an area of 260 square kilometers around the sunken oil tanker.
“Oil is continuing to come out of the place where the ship sank. What we are doing is to send a task force to clean up the oil spill found on the sea surface,” said Zhi Guanglu, deputy director of the China Maritime Search and Rescue Center.
“The fundamental way to eliminate the pollution source is to salvage the wreckage.”
Of the 32 sailors aboard the ship, three bodies were recovered, with 29 others, who are all presumed dead, still missing.