(CNN) -- Tropical Storm Chanthu has slowed, but it's edging ominously closer to an area of southern China already deluged with rain and deadly floods.
"The situation is grave," said China's State Council, or cabinet, according to the state-run Xinhua news agency. The council is urging local governments to step up flood control efforts.
Xinhua, quoting newly released government figures, said torrential rains and floods this year already have been the worst in a decade, claiming the lives of 701 people and leaving 347 missing,
Now, Chanthu could drench some already rain-swollen areas with another 20 inches, or half meter, of rain, according to CNN Weather Anchor Jenny Harrison.
Harrison said Chanthu has slowed over the last 24 hours and now is expected to make landfall Thursday evening, local time. It's moving north-northwest at five miles an hour and is expected to come ashore between Guangdong's coastal city of Yangjiang and Hainan's Qionghai City. But Hong Kong, to the east, also is expected to feel the storm's fury, as well as northern Vietnam.
Chanthu already has been pounding Hainan Island, off the coast, with sustained winds of 68 miles an hour and gusts reaching 87 miles an hour.
But as the storm moves inland, an area of particular concern is the region along the Yangtze River, which already has experienced the worst flooding in 30 years. Floodgates on the Three Gorges Dam have been opened to control the flow, and pictures from the scene show huge volumes of water pouring from it.
Throughout the country, floods have hit 27 provinces and municipalities, affecting 110 million people, according to Xinhua. It said more than 8 million people have been relocated.
About 287,000 military personnel have been mobilized in anti-flood operations, and schools are being advised to do what they can to ensure students' safety.
Xinhua also said the Qiongzhou Strait between the Chinese mainland and Hainan island was closed Wednesday as Chanthu headed toward south China. People in the affected areas are being advised to shut doors and windows and avoid outdoor activities.