ISTANBUL: Turkish authorities have detained nine of the 10 crew of an oil tanker after it collided with a cargo ship that sank off Istanbul, state media reported Thursday.

The ALSU, an empty oil tanker, collided early on Wednesday with the Tugberk Imamoglu, a cargo vessel carrying rolled steel, 18 nautical miles off Silivri district on the western edge of Istanbul province.

Officials said the damaged cargo ship sank “very quickly” in about 900 meters of sea, with Turkish authorities continuing their search on Thursday for the missing 10 crew members.

The ALSU was not damaged in the collision, the cause of which was not immediately clear.

Anadolu news agency said nine crew members on the ALSU, excluding the cook, had been detained and had given statements to the police.

Search and rescue operations continued with 18 vessels, five helicopters, two unmanned aerial vehicles and an aircraft involved alongside a navy vessel conducting underwater searches.

The Tugberk Imamoglu is a 90-meter Turkish-flagged cargo ship built in 1990, according to the VesselFinder tracking website.

Authorities said it was carrying 4,200 tonnes of rolled steel sheets and reinforcing bars at the time of the collision.

The maritime directorate initially said the ALSU was carrying 3,000 tonnes of motor oil, but later said the tanker was empty, a detail confirmed by the Istanbul governor’s office.