Three people were rescued so far. About 30 professional vessels, including patrol boats and tug boats, have been dispatched to search for the 22 missing people near the spot where the boat sank, state-run Xinhua news agency reported.
Rescuers are trying to stabilise the capsized boat and lift it out of the water by crane. However, rescue work has been difficult due to the swift current and cold water.
Wang Zhenkai, one of the three rescued, told Xinhua reporters that he was the interpreter for a 60-year-old Japanese engineer.
"Only the two of us were in the cockpit. We had just finished the load test of the boat's main engine when the vessel suddenly turned on its side. Water immediately flooded in," he said.
Wang, from Yantai City, Shandong Province, was saved after rescuers cut through the bottom of the boat. He has been hospitalised and was said to be in stable condition. He survived by clinging to a hydraulic pump.
Wang said he grabbed the Japanese engineer, but later the current broke their grasp as the boat started to sink. Zhang Lei, vice governor of Jiangsu, and Li Shixin, vice director of the National Maritime Bureau, are overseeing the on-site rescue work.
Diplomatic staff have arrived to help verify the identities of the foreign nationals on board the vessel. The 30-meter-long boat weighing 368 tonnes, was manufactured by Anhui Bengbu Shenzhou Machinery Company Limited in October. The company did not report the vessel's route or testing plans to port authorities, Xinhua said.