Two Turkish-flagged commercial vessels collided in the Sea of Marmara off Istanbul early Wednesday, with one ship believed to have sunk and its 10 crew members missing, authorities said.The chemical tanker Alsu, carrying around 3,000 tonnes of engine oil, collided with the bulk carrier Tugberk Imamoglu, which was carrying about 4,200 tonnes of coiled steel, near Istanbul’s Silivri district at around 3 a.m. local time.The Tugberk Imamoglu was en route to the Black Sea port of Karadenizeregli, while the Alsu was heading towards the Aegean port of Aliaga.Turkey’s maritime affairs authority said its rescue centre received an emergency signal from the Tugberk Imamoglu at 3:26 a.m.

The captain of the Alsu reported the collision about 15 minutes later.Authorities were unable to establish contact with the Tugberk Imamoglu or its 10 crew members. The ship failed to respond to repeated calls and its crew could not be reached on their mobile phones, leading authorities to assess that the vessel had sunk.One helicopter and 14 coastguard vessels were deployed in the search-and-rescue operation. The Istanbul governor’s office said there was no visible damage to the Alsu.

The Tugberk Imamoglu is owned by Zeybe Denizcilik, while the Alsu is operated by Ozpulathane Deniz Tasimaciligi, according to data from the Istanbul Chamber of Maritime Commerce.

The search-and-rescue operation was continuing, the governor's office said.