Emergency responders were still working on recovery efforts at Nippon Dynawave Packaging Company in Longview, the Longview Fire Department said.

Cowlitz Fire and Rescue Chief Scott Goldstein later told a news conference that it was unclear how many workers had been killed. Asked how many remained missing, he replied: "We have information on that, but we are not releasing that information."

Among those injured was a responding firefighter. Authorities said some victims had suffered burns or inhalation injuries, and that the severity of the injuries ranged from minor to critical. There was no immediate threat to the public, they said.

The statement, issued more than four hours after the tank imploded at 7:15 am, said crews were continuing recovery operations and that no identifying information would be released about victims pending notification of relatives.

The Nippon Dynawave Packaging Company facility is a pulp and paper mill and liquid packaging plant along the Columbia river in Longview, a city of about 38,000 that has had a relationship with the paper and lumber industries since its founding by a Kansas City timber baron in the 1920s.