Storm Kalmaegi has gained momentum as it approaches Taiwan, threatening the island's east, the Central Weather Bureau said Wednesday.

The edge of the storm may hit eastern Taiwan and unleash downpours in the east and north, an official at the bureau said.

"Ships sailing on the Bashih Channel and waters east of Taiwan must heighten their vigilance," the official said.

The storm was 370 kilometres (222 miles) southeast of Oluanpi, the island's southernmost tip, at 5:00 pm (0900 GMT).

Packing winds of 90 kilometres per hour, the storm was moving north-northwest at an hourly speed of 12 kilometres.