A series of earthquakes have been rocking the region in the past few weeks. Wikimedia Commons

An earthquake measuring 6.9 on the Richter scale struck off the volcanic Aleutian islands of Alaska late on Sunday (4.49am UTC Monday, 27 July).

The US Geological Survey said the quake occurred 100 km southwest of Nikolski, with the epicentre being 76 km southeast of Yunaska Island, the largest in the chain of islands.

There were no immediate reports of casualties or damage, Reuters said.

The quake struck at an estimated depth of 11.9 km.

The Pacific Tsunami Warning Center said there was no tsunami threat.

The Aleutian arc extends approximately 3,000 km from the Gulf of Alaska in the east to the Kamchatka Peninsula in the west.

It marks the region where the Pacific plate subducts into the mantle beneath the North America plate.

Most of the seismicity along the Aleutian arc results from thrust faulting that occurs along the interface between the two plates.

A 5.0 earthquake rattled south central Alaska on Saturday but did not cause major damage.