A 6.1-magnitude earthquake hit off Taiwan's east coast Friday morning, the United States Geological Survey said.

The tremor struck at 7:35 am (2335 GMT) at a depth of 15 kilometres (about nine miles) near Hualien, epicentre of a major quake in April, according to the USGS.

The island's Central Weather Administration, which initially reported a 6.3-magnitude quake, issued a mobile phone alert Friday morning warning people to "keep calm and seek cover nearby".

The National Fire Agency, which reported no damage, also urged vigilance after a 5.4-magnitude quake triggered a government alert on Thursday.

"In response to the continuous earthquakes, the Ministry of the Interior called on the public to remain vigilant, pay attention to the occurrence of aftershocks, and be prepared for earthquakes," it said in a statement.

Taiwan experiences frequent earthquakes due to its location between two tectonic plates.

The last major one occurred in early April, when it was hit by a deadly 7.4-magnitude tremor that officials said was the strongest in 25 years.

At least 17 people were killed in the quake, which triggered landslides and severely damaged buildings around Hualien.

April's earthquake was the most serious in Taiwan since it was struck by a magnitude-7.6 tremor in 1999.

Some 2,400 people died in that quake, making it the deadliest natural disaster in the island's history.