Nine employees remain missing after a chemical tank ruptured at a facility in Washington state, resulting in multiple critical injuries and at least one death, authorities said."Our community has entered a period of profound tragedy and deep mourning," Longview Mayor Erik Halvorson said at a press briefing Tuesday evening.Authorities said ongoing recovery efforts continue to be "extremely complex" due to the unstable tank, which contains white liquor, a chemical mixture used in the paper-making process.A photo obtained by the Cowlitz County News, a Facebook page run by local citizens, shows the aftermath of a tank rupture at Nippon Dynawave Packaging in Longview, Washington, May 26, 2026.Cowlitz County News/Facebook"The tank remains unstable creating a dangerous situation for our personnel," Cowlitz 2 Fire & Rescue Chief Scott Goldstein told reporters at a Tuesday evening press briefing.Fire authorities said the "hazardous materials incident" was reported Tuesday morning at Nippon Dynawave Packaging, a pulp and paper mill in Longview, a city of 38,000 people about 50 miles northwest of Portland.The tank ruptured at approximately 7:15 a.m., according to an earlier joint statement from local authorities and Nippon Dynawave Packaging.A photo obtained by the Cowlitz County News, a Facebook page run by local citizens, shows the aftermath of a tank rupture at Nippon Dynawave Packaging in Longview, Washington, May 26, 2026.Cowlitz County News/FacebookAuthorities initially referred to the incident as a chemical explosion and then an implosion, before referring to it as a rupture.Matt Amos, battalion chief for the Longview Fire Department, told reporters recovery efforts are set to resume Wednesday."Responders are continuing efforts to structurally reinforce and stabilize the site before additional recovery operations can safely proceed," authorities said in an earlier joint statement.Speaking at the Tuesday evening press briefing, Washington Gov. Bob Ferguson told reporters members of the Washington National Guard will assist with search and recovery efforts and with monitoring air quality.A photo obtained by the Cowlitz County News, a Facebook page run by local citizens, shows the aftermath of a tank rupture at Nippon Dynawave Packaging in Longview, Washington, May 26, 2026.Cowlitz County News/FacebookWhat we know about the victimsThere has been one confirmed fatality, a peron who had been taken to the hospital, authorities said.Officials have not publicly identified the person yet.Eight employees suffered injuries, including chemical burns, and were also transported by ambulance to area hospitals, authorities said. The injuries ranged from critical to minor, officials said during the earlier press briefing.One firefighter was also injured in the incident and has since been treated and released from a nearby hospital, according to authorities.Popular ReadsPatients with traumatic injuries were being treated at nearby medical facilities, while patients experiencing burns and exposure are being sent to other hospitals around the area, including in Portland, which are considered burn centers, Rick Graves, the spokesperson for Portland Fire and Rescue in Oregon, told ABC News.The Longview Fire Department in Washington state released this photo of the unstable tank that ruptured at the Nippon Dynawave Packaging facility on May 26, 2026.Longview Fire DepartmentPeaceHealth St. John Medical Center in Longview told ABC News it received nine patients from the incident -- including one deceased person. Six were in fair condition, and two other patients were transferred, it said.Legacy Health confirmed to ABC News it was treating patients in the incident, including at the Legacy Oregon Burn Center in Portland, though did not go into further detail.Police tape is shown at the scene of the Nippon Dynawave plant in Longview, Wash., after a hazardous materials incident, on May 26, 2026.KATUWhat's inside the tank?The damaged 900,000-gallon tank is estimated to still have 90,000 gallons of material inside, officials said. White liquor is a chemical mixture of sodium hydroxide, sodium sulfide and disodium carbonate used in the paper-making process, Goldstein said.Around the same time as the rupture in the tank, the facility also experienced a rupture in a water main on the site, Goldstein said. Approximately 500,000 gallons of the chemical mixture combined with the water but he said it has remained on the facility site.The cause of the rupture is unknown at this time, Goldstein said."We're dealing with life safety concerns and incident stabilization at this point," he said. "That will come in the hours and days to come."A vehicle from the Longview Fire Department is shown at the scene after a hazardous materials incident at the Nippon Dynawave plant in Longview, Wash., on May 26, 2026.KATUThere is no direct threat to the public, authorities said."The scene remains in the recovery phase as emergency responders continue operations," the joint statement said. "Responding agencies continue coordinating closely with facility personnel and partner agencies as the investigation and recovery efforts continue."Residents were urged to avoid the area amid the active emergency response.The Nippon facility is located on the Washington-Oregon border near the Columbia River. The kraft pulp and paper mill and liquid packaging plant employs nearly 1,000 people, according to the Washington Department of Ecology.ABC News' Trevor Ault, Alyssa Pone and Jack Moore contributed to this report.