The storm also sparked the evacuation of about 1.4 million people from Zhejiang and neighbouring coastal province Fujian, Chinese authorities said.
Al Jazeera's China correspondent, Tony Cheng, said many areas had been evacuated but many people were still in the storm's path and since the buildings collapsed at a late hour when people would have likely been home, casualty figures were bound to rise.
Morakot weakened to a tropical storm as it moved inland but our correspondent said it appeared the rains were doing the worst damage.
Many of the areas are mountainous and building standards are not known to be very high there, leaving many vulnerable to landslides, our correspondent explained.
Morakot killed at least six people and left three others missing in its wake elsewhere in China, flooding hundreds of villages and towns and causing more than 2,000 houses to collapse, Xinhua said.
Taiwan village buried
Morakot had earlier triggered the worst flooding in 50 years in Taiwan.
|Hundreds of people are believed to be buried under mud in Taiwan village Hsiao Lin [Reuters]
Al Jazeera's Steve Chao, reporting from southern Taiwan on Tuesday, said tens of thousands of people in the mountainous region had been cut off for more than 48 hours after roads and bridges were washed away or severely damaged.
Hundreds of people remained missing in Hsiao Lin and were feared to be buried in their homes after torrential rains caused a massive mudslide to sweep through the mountain village and envelop at least 200 homes, our correspondent said.
A massive rescue operation by the military was under way, he added, but collapsed bridges and washed-out roads were hampering efforts.
Some survivors who were lifted out by helicopter recounted horror stories of entire families being swept away.
Villagers were surprised by the typhoon as it had been forecast to track north but instead headed south to unprepared areas, our correspondent explained.
Dozens have been reported killed across the country.
Morakot, which means "emerald" in Thai, also lashed the Philippines earlier last week, killing at least 21 people there.