Tremors were felt across the island and high-rises in Taipei swayed as the quake struck off the northeastern coast at dawn, waking sleeping residents.

A 60-year-old woman was killed outside the capital after a closet fell on her during the quake, the National Fire Agency said.

More than 10,000 houses around the greater Taipei area and neighbouring Yilan lost power, while rail authorities suspended some train services in Yilan affecting thousands of passengers.

Taiwan was already on alert for typhoon Lekima, which is gaining momentum and is expected to buffet the island with powerful winds and heavy rains through to Friday.

"We will continue to monitor if there could be a combined impact from the aftershocks of the earthquake and the approaching typhoon," President Tsai Ing-wen told reporters.

Taiwan lies near the junction of two tectonic plates and is regularly hit by quakes.

In April, a 6.1-magnitude earthquake struck eastern Hualien, disrupting traffic and injuring 17 people.

Taiwan's worst tremor in recent decades was a 7.6-magnitude quake in 1999 that killed around 2,400 people.