NANJING - By Friday morning, rescuers have rescued three passengers on board a tug boat that sank on the Yangtze River in east China's Jiangsu Province on Thursday, and are still searching for more than 20 missing.

Seven or eight foreigners including Singaporean, Indian and Japanese nationals, are believed to be among the missing when the tug boat with 24-25 people on aboard sank while testing water in Fubei Channel on the Yangtze River at about 3 p.m. Thursday, local authorities said Friday morning.

Rescuers said the rescue work is difficult as the current is swift and the water is cold.

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 also arrived to help verify the foreign nationals on board the vessel.

Rescuers believed that there are people trapped in the cabin. The rescue team is trying to use crane to lift the inverted sunken boat out of the water.

Meanwhile, 23 vessels including patrol boats and tugging boats have been dispatched to search for the missing in area where the boat sank.

Wang Chenkai, one of the three rescued, told Xinhua reporters that he was the interpreter of a Japanese engineer.

"Only the two of us were in the cockpit. 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," he said.

He survived by clenching on a hydraulic pump. For a moment, he took hold of the Japanese engineer but later a swirling current broke up their clenching, as the boat started sinking.

The boat was manufactured by Anhui Bengbu Shenzhou Machinery Co. Ltd. in October. The producer did not report to port authorities for the water-testing operation and the vessel cruising route.