The westernmost inhabited island of Okinawa lies around 100 km from the east coast of Taiwan.
The local government said while no specific guidance had yet been issued, people should take the usual precautions.
“It is possible that strong winds will blow things around leading to broken windows and the risk of injury,” an official said.
“The local government may issue instructions and orders as the typhoon closes in,” he added.
The Hong Kong Observatory has classified Soulik as a “super typhoon” on its website, while Taiwan’s weather bureau listed it as a “strong typhoon”.
On the Chinese mainland, meteorological authorities maintained an orange alert the second highest level for Soulik on Thursday, Beijing’s official Xinhua news agency reported.
After hitting or passing Taiwan on Saturday Soulik is expected to head towards the coastal provinces of Zhejiang and Fujian, bringing “extremely strong” winds, it cited the National Meteorological Center as saying.
In August 2009 Typhoon Morakot killed about 600 people in Taiwan, most of them buried in huge landslides in the south, in one of the worst natural disasters to lash the island in recent years.