Five elderly people, three of whom fell due to strong winds, suffered non-life-threatening injuries in Okinawa while another person was injured in Kagoshima prefecture, authorities said on Saturday.
Almost 39,000 buildings were without power in Kagoshima while just more than 12,000 were affected in Okinawa.
Domestic airlines, ANA and Japan Airlines, cancelled flights to and from Okinawa.
The typhoon had maximum sustained winds of 162km/h with gusts reaching 216km/h.
Okinawa and Amami island in Kagoshima prefecture are the main areas expected to be affected in Japan.
In China, where the typhoon is expected to make landfall between late Sunday and early Monday, authorities have designated Dolphin as an orange-category typhoon - the second-highest level.
Worried about the risk of flooding and landslides, authorities also raised the emergency response level for Dolphin by one notch to level III, the second-lowest level.
The typhoon is most likely to cross the coast between Zhoushan city in Zhejiang province and Fuding city in Fujian province and is expected to bring winds of 137km/h to 162km/h near its centre, according to China's National Meteorological Centre.
Rain and strong winds are expected to affect eastern China through August 12, including parts of Shanghai and neighbouring provinces.
Some areas of eastern Zhejiang could receive more than 600mm of rain, according to forecasters.
Zhejiang raised its coastal typhoon alert to its highest level, halted port operations and suspended 162 passenger ferry routes.
Fujian also suspended ferry routes.
Ningbo Lishe International Airport in Zhejiang said it would halt operations late on Saturday and suspend all flights on Sunday.
Shanghai's Yangshan port had been cleared of vessels by late Friday, while some rail services in the Yangtze River Delta will be suspended from Sunday.
In Taiwan, 78 international flights were cancelled because of the typhoon, the government said.
Heavy rain was expected in northern parts of the island at the weekend, though authorities had not ordered evacuations as of Saturday.
China has ordered that, due to the typhoon, ships passing through the Taiwan Strait must heed its traffic control instructions - measures that Taipei denounced as "ridiculous", saying that Beijing has no right to restrict access to international waters.
China views democratically governed Taiwan as its own territory and claims the strategic strait.
Both Taipei and Washington reject that claim.
