A NOAA satellite image shows Typhoon Soulik in the Pacific Ocean, on July 10, 2013.

"That means trees could be uprooted and roofs ripped off" if the typhoon struck the island without losing strength, a weather forecaster told AFP.

Soulik is moving west-northwest towards Taiwan at about 22 kilometres per hour, and could narrowly miss the island or make landfall on its northern tip sometime between late Friday and Saturday morning, the bureau said.

"The public must heighten their vigilance as the typhoon will certainly bring strong winds and heavy rains," the weather forecaster said.

The Taipei-based TVBS news channel said the typhoon was moving along the same route as 1996 super-typhoon Herb which left 51 dead and 22 missing.

Taiwan's Central Weather Bureau is expected to issue a "land warning" at 1230 GMT, a warning signal issued when the storm is thought to be 18 hours away from Taiwan.

Authorities evacuated 2,300 tourists from Green Island, off the southeastern city of Taitung, and issued a warning to ships sailing north and east off Taiwan to take special precaution.

The Central Emergency Operation Centre also asked the public to stay away from the mountainous areas in central Taiwan, the epicentres of two recent earthquakes measuring more than 6.0 magnitude.

"The soil in the areas has been loosened after the two strong quakes and are prone to landslides," it said in a statement.

The Okinawa weather bureau in Japan warned waves of up to 12 metres and gusts of winds up to 234 kilometres (145 miles) per hour may hit parts of the far southwest of the archipelago.

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 because its wind speeds exceed 185 kilometres per hour, 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.