After the collision, the 80-meter-long Ukrainian tugboat, Naftogaz-67, sank in the South China Sea. The vessel had 25 crewmembers on board. Seven sailors were rescued, but the remaining 18 are missing.
"Their chances of survival are very slim," a spokesman for the Guangzhou rescue center said.
The 150-meter-long Chinese dry-cargo vessel suffered minor bow damage and remained afloat.
Initial rescue efforts were hindered by strong currents, and after nine attempts rescue workers failed to enter the hull of the sunken ship.
According to a local rescue official, a Chinese salvage boat was attempting to move the Ukrainian tugboat to shallow waters in order to ease rescue efforts.
The Ukrainian ambassador and consul-general in China are reported to have flown to the site of the incident.