Longview, Washington – A chemical incident at a paper plant in Washington state has killed two people. Officials said Wednesday that nine others are missing and feared dead.

The implosion of a huge tank holding tens of thousands of gallons of a highly caustic substance at a paper plant in Longview, Washington state, on Tuesday sparked a major operation.

Two people have been confirmed dead, and efforts to rescue the nine unaccounted-for individuals have now been abandoned, Scott Goldstein of Cowlitz 2 Fire and Rescue said.

"We have declared this incident a transition from rescue to recovery as of this morning," he said in a press conference. Nine other people were injured.

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Goldstein said the accident at the Nippon Dynawave Packaging Company happened during an early morning shift change when a 900,000-gallon tank containing a large quantity of a substance called white liquor ruptured.

White liquor is a highly alkaline solution containing sodium hydroxide and sodium sulfide that is used to break down wood chips and create the pulp from which paper is made.

Washington Governor Bob Ferguson said the community of Longview, which has a population of around 40,000, was hit hard.

"We’re bracing ourselves for this being the deadliest industrial tragedy in modern Washington state history," he said.

"When you have a tragedy of that scale, the impacts on individuals, families, and on communities is profound."

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Vehicles, buildings, and equipment were damaged in the spill. Specialist firefighters are still trying to establish where the missing people are.

Pictures from the scene show an enormous tank that has crumpled and is listing.

Goldstein said officials believe around 25,000 gallons remained in the tank, but that it was stable. "We still have contingency plans in place and resources coming if we need to change to stabilizing and removing the tank," he added.

Nippon Dynawave Packaging, a subsidiary of Japan's Nippon Paper Group, says on its website that it produces 8 billion single-serve containers every year, supplying customers in North America, Asia, and around the world.