In the capital Taipei, buildings swayed for some 14 seconds and "as the earthquake was on the island, its strength was felt strongly," said Kuo Kai-wen, head of the Seismology Centre.

The tremor struck at 11:55 pm (1555 GMT) with its epicenter located one kilometre (0.6 miles) northwest of the northeastern coastal town of Nanao, 19.4 kilometres under the earth, it said.

Some residents in Ilan city, near Nanao, fled their homes after being awakened by the strong tremor, TVBS cable news network said, adding that the quake also triggered rock falls on to a highway.

The world's tallest building, the 508-metre Taipei 101, remained intact, passing a key safety test, and the capital city's mass rapid transit system was not interrupted, TVBS said.

There were no immediate reports of casualties.

The destructive force of the quake was greatly reduced by the sea, the seismological centre added.

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