A strong but deep 7.7 magnitude earthquake struck off the Northern Mariana Islands in the western Pacific on Saturday, but triggered no tsunami alert, US monitors said.

The quake struck at a depth of 132 miles (212 kilometers) at 7:18 am local time (2118 GMT Friday) some 19 miles southwest of the island of Agrihan, according to the US Geological Survey.

No tsunami warning was issued.