ISTANBUL (Reuters) - The first vessel that used Ukraine's Black Sea corridor is crossing through Turkey's Bosphorus Strait, a Reuters witness said on Friday.

The Hong-Kong-flagged Joseph Schulte container ship that left the Russian-blocked Ukrainian Black Sea port of Odesa earlier this week had been in the port since Feb. 23, 2022, the day before the start of Russia's full-scale invasion of Ukraine.

Ukraine last week announced a "humanitarian corridor" in the Black Sea to release cargo ships that have been trapped in its ports after the termination of the main grain exports deal last month.

Moscow has not indicated whether it would respect the shipping corridor, and shipping and insurance sources have expressed concerns about safety.

Ukraine said the corridor will be primarily used to evacuate ships that were stuck in Ukrainian ports.

Local broadcasters have said the ship will anchor at Ambarli port in the south of Istanbul.

(Reporting by Murad Sezer; Editing by Kim Coghill and Raju Gopalakrishnan)