The Ukrainian tug, Naftogaz-67, sank after colliding with a Chinese vessel near Hong Kong off the southern coast of China. Out of the 25 sailors on board, only seven have been rescued.
A total of 44 Chinese divers will now be involved in the operation to find the missing sailors.
However, the South China Sea Rescue Bureau said it would not be instructing its divers at this stage to enter the sunken vessel due to the poor visibility and lack of knowledge of the ship's layout.
Earlier attempts to pull the Naftogaz-67 to shallow waters failed, as the ship's mast is embedded seven meters into the seabed, fixing the 2,723-ton vessel.
China will dispatch Asia's largest floating crane to the area by Friday. The crane was used late last year to raise the Nanhai 1, which sank 800 years ago.
Meanwhile, Anatoliy Prisyazhnyuk, the owner of the Ukrainian vessel, blamed the Chinese dry cargo ship for the collision.
"The Chinese dry cargo ship should have let [Naftogaz-67] pass, but failed to do so," the Ukrainian businessman said.
Ukraine has sent a delegation of officials from the emergencies, transport and fuel and energy ministries to Siangan to look into the cause of the accident.
Rescuers have already performed numerous dives to the wreck, but have so far failed to find any of the missing sailors. A chief Chinese rescuer said if the sailors had found an air pocket, then they could remain in the water for about 12 hours in temperatures of around 17 degrees Centigrade (62 Fahrenheit).
