About 185 people were injured and five others remain missing, according to Taiwan's National Fire Agency.
Those killed included a mother and her 8-year-old daughter swept out to sea, the nation's Central News Agency reported, adding that the girl's twin sister is unaccounted for.
It's now China's turn to take a pummeling, with Soudelor making landfall Saturday night in Putian city, in the nation's southern Fujian province.
Soudelor weakened as it moved inland toward the northwest. It has maximum sustained winds of 85 kilometers per hour (52 mph) and gusts of up to 100 kph (62 mph), according to the U.S. Joint Typhoon Warning Center.
Soudelor made landfall in Taiwan early Saturday north of the city of Hualien. Many areas across the island received a heavy downpour, with meteorologists saying 40 inches of rain fell in Taipingshan over two days.
One city in northern Taiwan saw a 210 kph (131 mph) wind gust.
Authorities deployed more than 35,000 military personnel to relocate residents in vulnerable areas as the typhoon made its way across the Pacific Ocean.
Taiwanese airlines announced flight adjustments, canceling a number of domestic and international flights for Saturday, according to Taiwan's Central News Agency. Railways also suspended high speed and regular train services, the agency said.
The Central Weather Bureau warned 16 cities and counties that they were likely to experience intense rain and powerful winds.
Soudelor became the strongest storm on the planet so far this year
, with peak winds at 180 mph (290 kph), according to the Joint Typhoon Warning Center.
Storm chaser James Reynolds told CNN from southeastern Taiwan that ferocious winds and blinding rain hit as the storm made landfall, as well as huge waves battering the coastline.
The result, he said, "was a lot of flying debris, a lot of tree damage and along the coastal areas, the waves had inundated the low-lying areas, damaging the roads in places as well as some vulnerable properties which were right by the coast."
Video footage showed rescue workers struggling to make their way through surging, thigh-high waters, as many communities suffered mudslides and flooding.
More than 725,000 homes were still without electricity Saturday night, with emergency crews working to restore supply, according to state power provider Taiwan Power Co.
Power outages have affected more than 4 million homes across the island, the company said, the biggest power outage seen on the island.
Storm bears down on China
In China, nearly 185,000 people have been moved to safer areas in Fujian province, which is expected to take a direct hit from the typhoon, state-run news agency Xinhua reported
Torrential rains over the next couple of days are likely to be a greater problem there than high winds. Heavy downpours in the course of the rainy season have already saturated the ground in some places.
Soudelor has already wreaked havoc in Saipan, Northern Mariana Islands, passing through this week, and disrupting water and electricity services.
The West Pacific Basin has seen 10 typhoons so far this year.
Of those, five have reached super-typhoon strength, meaning sustained winds of at least 150 mph (240 kph). That total is higher than the average of four for an entire year.