The Sierra Leone-registered ship, Razoni, set sail from Odesa early on August 1 carrying 26,000 tons of corn.
Turkey says the first ship carrying Ukrainian grain under a UN-brokered deal to lift Moscow's naval blockade in the Black Sea is expected in Istanbul "after midnight."
The Sierra Leone-registered ship, Razoni, which set sail for the Lebanese port of Tripoli from Odesa early on August 1 carrying 26,000 tons of corn, had been originally expected to arrive in Istanbul on August 2 in the early afternoon.
The Razoni had initially progressed slowly at just seven knots in Ukrainian waters due to possible mines but was then able to pick up speed, the Marine Traffic website said.
According to the website, as of 8 a.m. GMT the Razoni was moving southward along the Bulgarian coast some 50 kilometers off the port of Burgas.
It will be inspected by a special joint coordination center set up last week and staffed by civilian and military officials from both Ukraine and Russia, as well as delegates from Turkey and the UN.
In line with agreed procedure, the inspections will not take place in Istanbul's port itself, but at sea, at the mouth of the Bosphorus.
Media have been warned to stay away from the vessel.
An unnamed senior Turkish official told Reuters on August 2 that Ankara expects roughly one grain ship to leave Ukrainian ports daily as long as the UN-brokered agreement holds.
The departure of the Razoni was hailed by the international community, with UN chief Antonio Guterres "warmly" welcoming the move and NATO Secretary-General Jens Stoltenberg thanking alliance member Turkey for its "pivotal role."
However, Ukrainian President Volodymyr Zelenskiy said late on August 1 in his nightly address that it was too soon to celebrate.
"At this time, it is too early to draw any conclusions and make any forecasts," Zelenskiy said. "Let's wait and see how the agreement works and whether security will be really guaranteed."