At least one person has been killed and nine others are still missing after a major chemical explosion at a paper mill in Washington, authorities said.

The explosion occurred at 07:15 PDT (15:15 GMT) at the Nippon Dynawave Packaging facility in Longview, 130 miles (210km) south of Seattle.

A further nine people have been injured in the spill, including 8 employees and one firefighter, the Longview Fire Department said Tuesday evening, adding that the tank remains unstable.

The explosion occurred due a “rupture of a tank containing white liquor”, the company said in a statement. White liquor is a highly corrosive chemical used in the paper-making process.

“Recovery efforts remain complex due to ongoing safety concerns at the site,” the fire department said in an evening update.

“Currently, the tank remains unstable, creating hazardous conditions for emergency personnel,” the statement continued. “Responders are continuing efforts to structurally reinforce and stabilize the site before additional recovery operations can safely proceed.”