At least two people were killed and nine workers are "unrecovered" following the implosion of a chemical tank at a pulp and paper mill in southern Washington state on Tuesday, according to a news release shared by authorities on Wednesday afternoon. Several more people were injured. 

The tank ruptured at Nippon Dynawave Packaging Co. facility in Longview, a city located along the southern Washington border with Oregon, on Tuesday. 

On Wednesday, officials said the rescue effort had officially shifted to a recovery operation. The Washington Department of Ecology said that nine individuals who were previously described as missing "remain unrecovered" as of Wednesday. The department did not say if the unrecovered individuals were presumed dead, but said that "recovery efforts" were ongoing Wednesday and the scene remained "extremely hazardous."

"This was a blast. We've used the word explosion. We've used the word implosion. I've used the word failure. Indeed, there was a rupture, a failure, a blast," Cowlitz Fire and Rescue Chief Scott Goldstein said Wednesday afternoon. "All of those to us mean the same. It's not why it happened. It's the damage that we observe."

Authorities couldn't say how long the recovery would take, and they are not sure where all nine missing employees are.

The department said that all individuals "will undergo decontamination before being transported" to the Cowlitz County coroner's office "for identification and family notification." A list of victims will be provided when the individuals are recovered and their families notified, the department said.

As of Wednesday, none of the victims had been publicly identified. However, the family of Gilbert Bernal identified him as one of the deceased in several social media posts and released a statement saying they were waiting for his body to be released, calling him "an amazing husband, father, grandfather, son, brother and friend. Our family truly will never be the same."

A spokesperson for PeaceHealth St. John Medical Center in Longview confirmed to CBS News that the hospital received nine patients from the incident, one of whom was deceased. Four others had been transferred to the Legacy Oregon Burn Center in Portland, Oregon, PeaceHealth said. Legacy Health told CBS News in an update Wednesday that of the four patients, one was treated and released, two remain hospitalized, and the fourth died from their injuries. 

Authorities said some victims had suffered burns or inhalation injuries, and that the severity of the injuries ranged from minor to critical.

Authorities said there was no immediate threat to the public, but the tank's unstable condition is "creating hazardous conditions for emergency personnel."

Goldstein also stated Wednesday that "contamination entered the Columbia River," but that more testing was being done to better understand the scope of the contamination. They said testing indicated the drinking water in the surrounding area was safe. Washington Gov. Bob Ferguson said Wednesday afternoon there was no indication of air contamination.

The Longview Fire Department said a tank containing white liquor had ruptured. White liquor is a chemical commonly used in paper and pulp processing, which consists of sodium hydroxide and sodium sulfide.

Concerns about the structural integrity of the tank delayed recovery efforts, the department said. Authorities said the tank had an approximate capacity of 900,000 gallons, and was about two-thirds full at the time of the incident. 

Local authorities estimated Wednesday that roughly 25,000 gallons of material may remain inside the damaged tank, and it is leaking out slowly. An earlier inspection "revealed the remaining product is a significantly smaller volume, allowing emergency responders to develop a plan to move forward to remove it," the department said. 

Officials have still not determined the cause of the implosion. Goldstein said Wednesday that authorities are not aware of the implosion being captured on video.

The Nippon Dynawave Packaging Co. facility is a pulp and paper mill and liquid packaging plant that makes material for tissues, printing paper, cups, plates, cartons and other goods. It employs about 1,000 people, according to the Washington State Department of Ecology.

About 40 firefighters and paramedics had responded, along with a regional hazmat team, Gorsuch said. The incident was reported at 7:19 a.m. local time. Environmental monitoring and mitigation efforts continue, the department said, and the U.S. Environmental Protection Agency is assisting state authorities. The department said that as of Wednesday, there are "no negative health impacts to air quality or the City of Longview's drinking water system," but noted that the public should avoid ditches and dikes in the city while water testing is conducted. 

Nippon Dynawave did not immediately respond to a request for comment.

Meanwhile, thousands of Southern California residents remained evacuated on Tuesday due to a damaged chemical tank at an aerospace plant.