Authorities say the death toll has risen to more than 110 after a powerful undersea earthquake triggered a tsunami that hit South Pacific islands.

The majority of the fatalities occurred in Samoa, where rescue workers say at least 84 people have been killed. 

Another 24 people are confirmed dead on American Samoa, while at least seven fatalities have been reported in nearby Tonga. 

Samoan Prime Minister Tuilaepa Sailele Malielegaoi says he is shocked by the devastation. He added "so many people are gone."

Meanwhile, U.S. President Barack Obama has declared a major disaster in American Samoa and is sending federal aid to support local recovery efforts in the U.S. territory.

In a Wednesday statement, Mr. Obama also said the U.S. is ready to assist "friends" in Samoa and the neighboring region.

The U.S. Geological Survey says the powerful earthquake with a magnitude of 8.0 struck early Tuesday local time.

They say it generated waves that devastated coastal areas, knocked down buildings and sent cars floating out to sea. 

Strong aftershocks followed the initial earthquake, with at least one measuring a magnitude 5.6. Tsunami alerts were issued for the entire South Pacific region but were later canceled.