Three passengers -- all Chinese citizens -- have been rescued and the search operation continues, an official from the search and rescue office of the Jiangsu Maritime Administration told CNN.
Those rescued included an interpreter and the suppliers of some of the equipment on board.
The boat , which had 25 people aboard, was "testing water" in the Hubei channel, China's Xinhua
state news agency said.
Among the 25 on board were eight foreign nationals, the China News Service reported
Rescuers said their efforts were hampered by strong currents and cold water, Xinhua said.
As many as 23 vessels were involved in search and rescue operations, including a crane that is being used to lift the boat -- which turned over as it sank -- out of the water.
Rescuers believe that there are several people trapped in the boat's cabin.
One of the rescued passengers, identified as translator Wang Chenkai, told Xinhua that he tried to hold onto one of the Japanese engineers but the current broke his grip.
"Only the two of us were in the cockpit," he said. "We have just finished the host load test of the main engine of the boat, when the vessel suddenly slid over. Water immediately filled in."
Xinhua reported that the owner of the boat had not followed procedure for the water-testing operation and had not filed a route.