A chemical incident at a paper plant in the northwestern US has killed two people, with nine others missing and feared dead, officials have said.
"We're bracing ourselves for this being the deadliest industrial tragedy in modern Washington state history," Washington Governor Bob Ferguson said at a news conference with local authorities.
Authorities said they do not yet know what caused a 900,000 gallon vat at the Nippon Dynawave Packaging facility to implode early on Tuesday.
The container held "white liquor" - a chemical solution of sodium hydroxide and sodium sulfide used in making paper pulp that can cause severe burns on skin.
Longview Fire Department Battalion Chief Matt Amos said at the news conference the recovery effort would proceed slowly in the "extremely hazardous" environment.
It was unclear where exactly the nine missing people were in the facility, Cowlitz 2 Fire Chief Scott Goldstein said.
He added that they had searched the area that was searchable.
"As of this morning, we declared this incident a transition from rescue to recovery," he said.
Authorities at the press conference said that testing confirmed that contamination entered the Columbia River.
Mr Goldstein said: "Testing of water samples has confirmed contamination entered the Columbia River during the day yesterday.
"Additional evaluations are under way to better understand the scope and extent of that environmental impact.
"At this time, there ... continue to be no identified negative health impacts to ... the surrounding air quality or the city of Longview's drinking water system."
He said it was fair to say roughly 550,000 - 570,000 gallons left the tank, while some material remains in the tank and is continuing to slowly leak.
Officials advised people to stay away from parts of the area and said that about a dozen carp had died.
Nippon Paper Industries (3863.T), Japan's second-biggest paper manufacturer by sales, acquired the Longview plant from Seattle-based timber company Weyerhaeuser (WY.N) for $225 million (€194 million) and established the wholly-owned subsidiary Nippon Dynawave Packaging in 2016.
In southern California, meanwhile, authorities who had been monitoring an overheating industrial tank containing highly flammable methyl methacrylate said late Tuesday that the GKN Aerospace facility in Garden Grove no longer posed a risk of explosion.
Thousands of people had been ordered to evacuate their homes in the area last Thursday after the chemical in the tank was found to be overheating.
"After an extensive operation, we're happy to report that all evacuation orders have been lifted and residents have started to return home," TJ McGovern, interim chief of the Orange County Fire Authority, said on Tuesday.
