SAN FRANCISCO, May 26 (Xinhua) -- The implosion of a chemical tank at a pulp and paper mill in Longview, the U.S. state of Washington, killed an undisclosed number of people and left multiple others critically injured, local authorities and company officials said Tuesday.

In a joint statement posted on social media, Nippon Dynawave Packaging Company and local authorities said that a rupture of the tank caused "multiple critical injuries" and fatalities. The exact number of deaths has not been released.

The Longview Fire Department earlier said it was responding to a hazardous materials incident involving the implosion of a vat of chemical treatment product at the Nippon Dynawave facility. Multiple people suffered chemical burns and other injuries and were transported to hospitals.

Officials said there was no ongoing threat to the public, yet residents were urged to stay away from the area while emergency crews worked at the scene.

The facility is located near the Washington-Oregon border along the Columbia River. According to the Washington State Department of Ecology, it is a kraft pulp and paper mill and a liquid packaging plant.

The cause of the incident remains under investigation.