An earthquake measuring 4.1 on the Richter scale hit the northern mountainous province of Lai Chau 's Sin Ho district on April 28.

Residents at the epicentre might have felt slight vibrations, according to the vice president of the Geophysical Institute, Le Huy Minh.

It was the third tremor to hit Lai Chau in the past four days.

Lai Chau lies in a high risk earthquake area, Minh added.

He also said local authorities and residents should prepare for future earthquakes. /.