Washington state authorities have declared a state of emergency as unprecedented flooding triggered by an atmospheric river and prolonged heavy rainfall inundates communities, destroys infrastructure and prompts large-scale evacuations.

Rivers across western Washington, including the Skagit, Snohomish and Snoqualmie, have surged to record or near-record levels, flooding residential neighbourhoods, closing major highways and cutting power to tens of thousands of homes.

Emergency operations centres have activated search and rescue teams, and helicopters are retrieving residents stranded on rooftops in towns such as Sumas and Mount Vernon as waters continue to rise.

Governor Jay Inslee signed the emergency declaration to unlock additional state and federal resources, mobilise the Washington National Guard and support local authorities in rescue and relief efforts.

The declaration accelerates funding and logistical support for shelters, medical care and critical infrastructure repairs.

Federal officials have signalled their readiness to coordinate disaster assistance and assessments that could lead to a broader federal disaster declaration if the scale of destruction meets the criteria.

Forecasters warn that additional precipitation is expected in some areas, heightening the risk of further riverine flooding, landslides and infrastructure damage.

Transportation networks have been severely affected, with closures on Interstate 90, U.S. Route 2 and other key corridors as crews work to clear debris and stabilise slopes.

Emergency services caution residents to avoid flooded roads and heed evacuation orders, noting that floodwaters can conceal hazards and sweep vehicles off their routes.

Utilities are prioritising restoration of critical power and water services, but officials warn that outages may persist in hard-hit communities.

Shelters established in safer zones are accommodating displaced families, and volunteer organisations are coordinating distribution of food, clothing and medical supplies.

The scale and intensity of the flooding have drawn comparisons to some of the state’s worst historical flood events, underscoring the challenges that atmospheric rivers — intense bands of moisture-laden air — pose to infrastructure and emergency management.

Authorities continue to monitor levees and critical flood defences, even as relief operations expand.

Officials emphasise that community cooperation with evacuation directives and safety guidance remains essential as the region navigates an evolving and dangerous flood crisis.