SARTELL -- Saying it's "a very sad day for our Verso family," the plant manager of Sartell's Verso paper plant says the cause of a massive explosion earlier today is still unknown.

Matt Archambeau spoke at a news conference tonight at Sartell City Hall after an explosion rocked his plant just after 11:15 this morning.

He's asking for people to stay away from the site while crews continue to work to put out a fire at the plant. The fire is contained to the warehouse area and still burns this early evening.

Sartell City Administrator Patty Gartland confirms one death and five injuries (new number). A St. Cloud Hospital spokeswoman says three of those injured have been treated and released.  One was still in the emergency trauma center late this afternoon. The condition of a fifth person is not known.

The names of the dead and injured have not yet been released.

Fire crews from eight communities are working at the scene.

Sartell's fire chief Ken Heim calls the fire "the biggest in Sartell history."

The fire, Heim says, continues in the warehouse building which houses large rolls of paper.  He says the fire's about 90% contained, but the building is structurally unsound, and that's slowed efforts to put out the flames.  Heim expects fire crews will be on scene round-the-clock for "a day or two."

Heim says the State Fire Marshall is on-scene and the investigation will begin when the fire's out.

Officials will hold another news briefing at 8 a.m. Tuesday.  You can hear that news conference live on AM 1240 WJON.

Hear the news conference on-demand: