The casualties were reported in and around Wenzhou city in the province of Zhejiang, where downpours caused mudslides and several houses collapsed on Saturday night, Xinhua news agency reported.
It quoted local disaster relief officials as saying the dead and missing may have been washed away by floods or buried under ruined homes.
About 1.36 million people in the city were affected by the typhoon, the agency said, estimating direct economic losses at $617 million.
Read: Typhoon lashes China after more than a million people evacuated
Nearby Wencheng county saw downpours of 645 millimetres in 24 hours – the heaviest in 100 years – after the typhoon made landfall on Saturday night, it said.
The storm had landed in Fujian province and cut power to more than three million homes there, Xinhua said, but more than a third had electricity restored by Sunday morning.
Billed as the biggest typhoon of the year last week with winds of up to 230 kilometres an hour, Soudelor – named after a legendary Micronesian chief – has since weakened.
China's National Meteorological Center forecast the typhoon would be downgraded to a tropical depression by Sunday night as it moved further inland.
Soudelor left six people dead in Taiwan, where it ripped up trees and triggered landslides, damaging electricity lines and knocking out power to a record four million households.
Almost half a million homes were still without power Sunday, Taiwan Power Co. said, as blocked roads hampered efforts to restore supplies in some areas.
Read: Typhoon Soudelor churns towards China after killing five in Taiwan
Taiwan's death toll rose to six after an eight-year-old girl who went missing Thursday after being swept out to sea with her mother and twin sister was found dead.
Her mother and sister, caught in the strong waves on the east coast, were the first victims of the typhoon.
Some 379 people were injured by the storm in Taiwan, which saw rivers break their banks under torrential rain and towering waves pound the coastline.
Taiwan lifted its typhoon warning Sunday, but the weather bureau warned of further heavy rain in the south.
COMMENTS
Comments are moderated and generally will be posted if they are on-topic and not abusive.
For more information, please see our Comments FAQ