The boat crews were practising on Saturday for a race in the Taohua river in the city of Guilin when the accident happened, the city’s fire department said.
The accident happened where two flows of the river converge, causing a powerful current, the CCTV broadcaster said.
Television pictures showed one of the long, narrow boats packed with paddlers going over. Another dragon boat arrived at the scene, also full of paddlers, and it too capsized, the pictures showed.
Most of those who went into the river were not wearing life jackets, media reported.
The Guilin fire department said on the Sina Weibo social media site that search efforts ended late on Saturday and 17 people had been confirmed dead. A total of 60 people fell into the water.
The official Xinhua news agency said eight boats and more than 200 people had been deployed to the rescue.
Two organisers of the practice, from the village of Dunmu, were detained, Xinhua said.
The dragon boat festival, which this year is being held on 18 June, is a traditional holiday in China.
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