A preliminary study estimated about 500 tonnes (3,420 barrels) of oil had been spilled but this needs to be assessed further, a Shandong Maritime Safety Administration official who declined to be identified told Reuters by phone on Wednesday.

The Liberia-flagged tanker A Symphony was at anchor off Qingdao port with a cargo of around a million barrels of bitumen mix on board when it was involved in the collision with shipping vessel Sea Justice on Tuesday.

The accident took place about 11 nautical miles south-east of Qingdao port and the impact caused a breach in its cargo tanks and ballast tanks.

Ships have been instructed to stay at least 10 nautical miles away from the A Symphony.

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.