One person was killed and three others were injured in a landslide that prompted a mandatory evacuation in the Alaska city of Ketchikan, authorities said.

Three people were taken to Ketchikan Medical Centre following the landslide, which struck around 4pm local time on Sunday and damaged homes and infrastructure, the Ketchikan Gateway Borough and City of Ketchikan said in a joint statement.

Alaska Governor Mike Dunleavy declared an emergency for Ketchikan, while Borough Mayor Rodney Dial and city Mayor Dave Kiffer issued a separate emergency declaration.

“Friends, is with a heavy heart we relay that a landslide in the city has taken a life, caused several injuries, damaged homes and impacted our community,” Mr Dial said.

Mr Kiffer said the loss of life is “heart-breaking, and my heart goes out to those who lost their homes”.

“In my 65 years in Ketchikan, I have never seen a slide of this magnitude. With the slides we have seen across the region, there is clearly a region-wide issue that we need to try to understand with the support of our state geologist,” he added.

Two of the victims were admitted to hospital and one was treated and released. All other individuals have been accounted for, a statement said.

Multiple homes were hit by the landslide and a mandatory evacuation was ordered for residents of Third Avenue and nearby streets, while a shelter was set up at Ketchikan High School, the borough and city said.

A potential secondary landslide area was identified to the south of the original slide location and crews were standing by, the statement added.

Power was restored to some affected areas by 8.15pm. Other areas will remain without power while the landslide is cleared and broken power poles are replaced, the borough and city said.

Various local and state agencies responded. A Department of Homeland Security and Emergency Management Response Specialist and federal Department of Transportation personnel are expected to travel to Ketchikan on Monday, Mr Dunleavy said.

“I have directed state agencies to make available all resources and staff for the response effort,” he said, noting the city is receiving assistance from the State Emergency Operations Centre.