Crews are continuing to search for nine people who are still missing after a tank containing a highly-corrosive industrial chemical ruptured on Tuesday at a paper mill in Washington state.

But their mission has switched from rescue to recovery, as they do not expect to find any survivors.

Two people are so far known to have died, of whom one has been identified as Gilbert Bernal by his daughter, who paid tribute to the man's selflessness. Seven others were injured.

The scene "still remains active, and its extremely hazardous in the recovery environment", Matt Amos, battalion chief of the Longview Fire Department, said at a news conference on Wednesday.

A large volume of contaminants has entered the Columbia River, following the incident at the the Nippon Dynawave Packaging facility. But local drinking water and air quality remain unaffected, officials say.

Officials say the tank ruptured, spilling hundreds of thousands of gallons of white liquor, an alkaline solution used to make paper products. They say about 25,000 gallons remain inside the tank, but the chemical is still slowly leaking out.

Photos from the scene show the ruptured tank, as well as crushed and overturned vehicles.

"As individuals are recovered they will undergo decontamination before being transported to the Cowlitz County Coroner's Office for identification and family notification," said a joint statement issued by Longview Fire Department and Nippon Dynawave on Wednesday.

One injured person who was taken to hospital on Tuesday later died of their injuries, raising the confirmed death toll to two.

In addition to the seven employees who were hurt, a firefighter was also injured at the scene.

As for the group still missing, Cowlitz Fire and Rescue Chief Scott Goldstein said authorities "do not know where all nine are".

"We have searched the area - the area that is searchable," he said, adding that it is still too dangerous to venture into certain parts of the facility.

Fire battalion chief Amos added that crews were wearing special gear to protect them from chemicals, but "we do run into some industrial hazards [that] for any level of equipment wouldn't be safe for us to continue".

He said that operations will be "slow, methodical and deliberate... while treating every victim with the greatest dignity, care and respect as possible".

According to local media, the Nippon Dynawave Packaging facility was also the scene of a major fire in July 2023, when piles of wood at the site burned for days.

The plant makes tissues, printer paper, cups, plates, cartons, and other goods. It employees 1,000 people, according to the Washington State Department of Ecology.

Washington Governor Bob Ferguson said the explosion was the "deadliest industrial accident in modern Washington history", and he has deployed the National Guard to assist in the recovery and clean-up operations.

One victim has been identified by family members as employee and grandfather Gilbert Bernal.

His daughter Geovana Bernal said in a statement to ABC News that her father "was the most selfless man I knew. He worked hard to provide for his family and he loved us so much."

"He was going to celebrate his 32nd wedding anniversary with mom in just a couple weeks and he loved my son, his first grandson, so much."

She added that her brother identified Bernal's body through photos sent by the coroner's office.

The other victim confirmed deceased has not been identified.