BEIJING—A boat that capsized on a river in southwest China has left at least 10 people dead, with another five still missing, according to state media on Sunday. CCTV said that the ship overturned shortly after it departed Saturday evening in Guizhou Province. Preliminary investigations suggest that the ship was blown over by strong winds. The tragedy struck days before China’s annual Mid-Autumn Festival, when families traditionally gather to have dinner and mooncakes. Local authorities said the ship was overloaded when the accident happened. At least 46 people were on board, exceeding the maximum capacity of 40 people, according to CCTV. As of Sunday, rescuers had saved 31 passengers, state media said, with most of those on the boat thought to be students. Over a dozen rescue teams have been dispatched to join the search and rescue operation, according to the official Xinhua News Agency. The broadcaster added that rescue …