A massive earthquake of 7.4 magnitude hit Alaska's remote Aleutian Islands at 6:09 p.m. local time on Thursday.
The quake struke over 1,000 miles west of Anchorage.
A second quake of the same magnitude hit in the same vicinity and at the same depth 30 seconds later, the US Geological Survey said.
The United States Geologic Survey said it struck at a depth of about 24 miles in the Pacific Ocean.
A tsunami warning is now in effect which includes the coastal areas of Alaska from Unimak Pass, Alaska (80 miles northeast of Dutch Harbor) to Amchitka Pass, Alaska (125 miles west of Adak), stated the West Coast and Alaska Tsunami Warning Center.
Those feeling the earth shake, seeing unusual wave action or the water level rising or receding may have only a few minutes before the tsunami arrival and should move immediately, warned the West Coast and Alaska Tsunami Warning Center (WCATWC).
Homes and small buildings are not designed to withstand tsunami impacts. Do not stay in these structures, warned officials.
The WCATWC said if a tsunami had been generated, the waves would first reach Adak, Alaska, at 8.12pm local time.
No immediate reports of damage or injuries have been made.