Kong-rey's winds were sustaining maximum speeds of more than 230 kilometres (143 miles) per hour as it approached Taiwan, the US Joint Typhoon Warning Center said, slightly slower than an earlier reading.

The storm was expected to unleash "destructive" winds when it made landfall in the lightly populated southeast on Thursday, the state weather forecaster, Central Weather Administration, said.

More than a metre of rain could fall in the hardest-hit areas by Friday as the seasonal monsoon also drenches the island of 23 million people, prompting warnings of landslides and evacuations of thousands of people from their homes in vulnerable areas.

Kong-rey was currently more powerful than the deadly Typhoon Gaemi, which was the strongest typhoon to hit Taiwan in eight years when it made landfall in July.

"If (Kong-rey) keeps the current wind speed, it will be the biggest typhoon in eight years," Chang Chun-yao from the state weather forecaster, Central Weather Administration, told AFP.

Classes and work will be suspended in cities and counties across the island on Thursday, including Taitung county where the typhoon looks set to make a direct hit and generate storm surges of up to 14.5 metres high.

Dozens of ferry services and domestic flights were cancelled Wednesday.

Taipei residents planning to hunker down during the storm stocked up on fresh vegetables, while fishers wearing slickers against the rain tethered their boats in the harbour in Yilan county, southeast of the capital.

"Of course I'm worried. All my assets are here," a fisherman, who gave his name as Captain Chen, told AFP.

Kong-rey was expected to dump the heaviest rain on Taiwan's eastern and northern coastal areas, and over the mountains in the central and southern regions, the Central Weather Administration said.

Yilan and the eastern county of Hualien were expected to be hardest hit, with accumulated rainfall from Tuesday to Friday reaching 800 to 1,200 millimetres (31-47 inches), forecaster Chang told AFP.

"Based on the projected path of the typhoon, we advise Yilan, Hualien and Taitung to take precautions against potential landslides and debris flows in areas expected to receive heavy rainfall," Chang said.

Authorities began evacuations Wednesday in eight counties and cities, including Yilan, Hualien and Taitung, according to the National Fire Agency.

More than 6,200 people had been evacuated from their homes by the evening.

Interior Minister Liu Shyh-fang expressed concern at a meeting with disaster officials for the safety of two Czech tourists hiking in Taroko Gorge in Hualien after authorities said they could not reach them on their satellite and mobile phones on Wednesday.

- 'Moving fast' -

Kong-rey was moving at a speed of 20 kph and churning up waves up to five metres (16 feet) high around the shoreline, the state weather forecaster said.

With a radius of 320 kilometres, it was on track to be the most expansive "severe typhoon" to make landfall in nearly 30 years, the forecaster said.

In the Philippines, more than 174,000 people fled their homes as Kong-rey passed the northern island of Luzon.

Taiwan President Lai Ching-te urged people to stay alert and avoid going to the mountains or the sea.

"This typhoon is moving fast and will bring strong wind and torrential rain," Lai said on Facebook.

Taiwan is accustomed to frequent tropical storms from July to October, but forecaster Chang said it was unusual for such a powerful typhoon to hit this late in the year.

"The last occurrence was the Typhoon Nock-ten in October 2004," Chang told AFP.

Scientists have warned climate change is increasing the intensity of storms, leading to heavier rains and flash floods and stronger gusts.

Kong-rey will be the third typhoon to hit Taiwan since July.

Gaemi killed at least 10 people, injured hundreds and triggered widespread flooding in the southern seaport of Kaohsiung.

That was followed in early October by Krathon, which killed at least four people and injured hundreds, triggering mudslides, flooding and record-strong gusts.