Clean-up crews endeavored on Wednesday to contain an oil spill in the Yellow Sea near the Chinese port city of Qingdao, a day after a tanker carrying around a million barrels of bitumen mix and a bulk vessel collided in thick fog.

The size of the spill has yet to be determined.

“There are oil spill experts on the scene that have started clean-up operations,” said a spokesman for Goodwood Ship Management, manager of the Liberia-flagged tanker, A Symphony, which was at anchor when involved in the collision with shipping vessel Sea Justice. The impact caused a breach in its cargo tanks and ballast tanks.

The Shandong Maritime Safety Administration said on its Weibo account on Wednesday morning that the collision caused a “minor” spill.

It added that the two ships were in stable condition, there were no casualties and an investigation into the cause of the accident was under way. On Tuesday, it told vessels to stay at least 10 nautical miles from the A Symphony, but didn’t elaborate on how much oil has leaked.

An official from the Ministry of Ecology and Environment told Reuters on Wednesday that they had dispatched experts to Qingdao to check the spill but did not give more details.

Hong Kong-based fuel trading company Run Cheng International Resource (HK) Co has said it was the owner of the 150,000-tonne cargo of bitumen blend on board the A Symphony.

Bitumen mix, a blend of heavy crude oil and residue, is used by China’s independent refiners as an alternative refining feedstock as it often incurs a lower import tax than crude oil. It is also used for road surfacing and roofing.

The 272 metre-long and 46 metre-wide oil tanker was sold in May 2019 to its new owners Symphony Shipholding SA and NGM Energy, Equasis data revealed.