In rural Yilan county, where the typhoon will first hit land, heavy rain battered the countryside.
Work and school are suspended across the whole of Taiwan, with the streets of capital Taipei almost deserted during what is normally rush hour amid squally rain.
The transport ministry said almost all domestic flights had been cancelled, along with 27 international flights.
However, TSMC, the world’s largest contract chipmaker and major Apple supplier, said it expected all its factories would maintain normal production during the typhoon, adding it had activated routine preparation procedures.
Some mountainous central and southern Taiwan counties are expected to see total rainfall of up to 1,800mm during the typhoon, the weather administration said.
Taiwan’s defence ministry said it was ready to assist with disaster relief and had put its forces on standby.
While the typhoon has severely curtailed this year’s annual Han Kuang war games they have not been totally cancelled, with live fire drills taking place as scheduled on the Penghu islands in the Taiwan Strait on Wednesday morning.
Gaemi and a southwest monsoon brought heavy rain on Wednesday to the Philippine capital region and northern provinces, prompting authorities to halt work and classes, while stock and foreign exchange trading were suspended.
While typhoons can be highly destructive, Taiwan also relies on them to replenish reservoirs after the traditionally drier winter months, especially for the southern part of the island.
