One person was killed and nine others are missing after a chemical vat imploded at a paper mill in Washington state. 

Nippon Dynawave Packaging in Longview confirmed that multiple people suffered injuries when the toxic tank burst at 7.15am Tuesday. 

Mike Gorsuch, battalion chief with the local fire department, described what he saw as a 'mass casualty scene.' 

At least 10 people were taken to the hospital with severe injuries, including burns and inhalation damage, including the one fatality.

Among those who were injured in the implosion were eight employees at the pulp and paper mill and liquid packaging plant, as well as one firefighter. 

Several distressed relatives waited at the company's visitor entrance later on Tuesday, seeking information about loved ones who worked at the facility. 

Nippon Dynawave Packaging facility makes material for tissues, printing paper, cups, plates, cartons and other goods. 

Located in Longview just north of the Oregon border, it employs about 1,000 people, according to the Washington State Department of Ecology. 

The tank that imploded contained a chemical brew known as 'white liquor,' a corrosive substance that consists mainly of sodium hydroxide and sodium sulfide. 

The substance is used to break down wood to make kraft paper, a durable paper used in packaging, shopping bags and other products.

Photographs from the scene show the vat partially collapsed from the impact of the implosion, with smoke billowing in all directions. 

A van at the site was also shown partially crushed under a metal pipe, which had a liquid substance spraying from a crack. 

The tank held approximately 900,000 gallons of the corrosive substance, and Longview Fire and Cowlitz 2 Fire & Rescue estimate about 90,000 gallons of white liquor may remain inside the damaged tank.

'Currently, the tank remains unstable, creating hazardous conditions for emergency personnel,' the Longview Fire Department posted on Facebook on Tuesday evening. 

'Responders are continuing efforts to structurally reinforce and stabilize the site before additional recovery operations can safely proceed.'

Those recovery operations 'remain focused on safely accessing all affected areas of the facility, recovering victims and supporting impacted families, while ensuring the safety of emergency responders working within unstable conditions.'

But recovery efforts will not resume until Wednesday morning due to the ongoing safety concerns. 

Gorsuch, battalion chief with the fire department in Longview, Washington, said first responders had decontaminated patients. 

They were taken to hospitals in Longview and Vancouver, Washington.

About 40 firefighters and paramedics had responded, along with a regional hazmat team, Gorsuch said.

The cause of the explosion is unclear. A video from the scene shows ominous white clouds emanating from the facility in the aftermath of the implosion. 

Washington State Governor Bob Ferguson said the National Guard has been placed on alert. 

'My team and I are tracking developments in Longview closely after a major chemical explosion,' he added. 

'Responders from our state Department of Ecology have been deployed to the scene.'

I'm deeply saddened to hear that there have been fatalities. My thoughts are with the workers and their families, and with the first responders.

It comes after a tank containing a hazardous chemical was damaged at a Southern California aerospace plant, prompting mass evacuations. 

Officials ordered 50,000 residents to temporarily leave their homes, citing the risk of a catastrophic explosion. 

The storage tank at GKN Aerospace, containing about 6,000 to 7,000 gallons (23,000 to 26,500 liters) of methyl methacrylate, overheated last week in Garden Grove, a city in Orange County.

Officials have said the tank vented vapors as pressure and temperatures rose, but that monitoring has not detected hazardous chemical levels in the atmosphere. 

No injuries have been reported. 

While officials said Monday that an overnight inspection confirmed a crack in the tank relieved pressure and cooled the chemical, they said some risk to public safety remained, including a possible fire, spill or small explosion. 

Methyl methacrylate is a flammable, colorless liquid used in the production of resins, plastics and plastic dentures and is regulated by the federal government.

It can irritate the lungs, eyes and skin, and in high doses can cause reduced lung function, along with dizziness and memory problems, according to the Environmental Protection Agency.

In prolonged cases, exposure to methyl methacrylate can cause serious respiratory problems or render a person unconscious.

Tests have found that air pollution in the evacuation zone is within normal limits.