The explosion, sinking, and subsequent oil spill caused by Iranian oil tanker Sanchi in the East China Sea between China and Japan is now an “unprecedented” disaster in the region, a Chinese official said on Friday. The oil spill has now spread to cover an area the size of Paris.

The Sanchi collided with a local vessel on January 6, catching fire for days before exploding on January 10, presumably killing the dozens of Iranian crew members on board. Rescuers have found only three of 32 bodies. The ship was carrying a light crude product known as condensate, but was fueled by a heavier oil that experts worry could seep out of the sinking ship and exacerbate the environmental damage.

“There was no precedent for this accident,” transport ministry official Zhi Guanglu told reporters on Friday. “We are still facing enormous difficulties and many challenges.”

Zhi affirmed on Friday that the Chinese government would organize an extensive investigation into the cause of the accident.

“The Chinese government will continue to give priority to follow-up work. The State Council held a special meeting to study the accident and formed a trans-department team to look into it,” he said, according to the state-run Global Times newspaper.

China’s State Oceanic Administration is monitoring the spread of the condensate, which has created oil slicks that are taking up a total area of over 77 square miles, as per the latest available reports on Friday.

On Thursday, CNN reported that the slick was 38 square miles total, the size of the city of Paris.

Of pressing concern is the decision on whether to let the ship sink or attempt to salvage it from the water. While the condensate evaporates quickly, the ship was also using heavy bunker fuel to operate, which could pose an extreme environmental risk as it is thicker and more toxic. At least one of the many oil slicks surrounding the crash shows signs of bunker fuel in it, not just condensate. Reuters notes that officials do not know how much of this fuel remained in the ship when it first crashed or how much has leaked into the ocean already.

Zhi told reporters that China is weighing pulling the ship out to prevent more leakage, but that the operation could result in another explosion as “the residual condensate oil in the tanker could burn.”

“The tanker has sunk 115 meters, so the salvage mission would be very difficult,” Zhi explained.

The Chinese government will send robots in to assess whether a recovery mission is worth the risk.

Investigators have not yet identified a cause for the crash or ascribed blame for the accident. The left-wing environmental organization Greenpeace has issued a statement on the potential damage of the spill, but has not condemned Iran for the spill. The ship belonged to the National Iranian Tanker Company, which has become significantly more active since the Joint Comprehensive Plan of Action (JCPOA), or Iran nuclear deal, resulted in sanctions being lifted on the corporation.

Nonetheless, Greenpeace noted that the area affected is “an important spawning ground for many commercial species such as the bluefin leatherjacket (Thamnaconus septentrionalis) and the swordtip squid (Uroteuthis edulis).” During the winter months, the advocacy group noted, it is also home to a larger variety of marine life and serves as a maritime migration route for “humpback whale, right whale and gray whale.”

Both Iran and China have signed the Paris Agreement on climate change, which requires parties to “promote environmental integrity, transparency, accuracy, completeness, comparability and consistency.”

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