(CNN) — An accident at a silver mine in Colorado on Sunday morning killed two miners and left 20 injured, officials said.
The identities of the two miners — who were initially believed trapped — were not released.
Two of the injured were in critical condition, according to Jennifer Dinsmore, a spokeswoman for Ouray County.
The cause of the accident was not immediately known, though authorities have determined there was no explosion, Dinsmore said.
Rory Williams, project manager for the mine’s operator, told the Ouray Watch newspaper it was a “powder-smoke incident,” and those injured had inhaled chemicals.
The accident occurred at the Revenue-Virginius mine near Ouray, roughly 100 miles southeast of Grand Junction.
The mine produces silver, lead, zinc, copper and gold, according to the company website.
CNN’s Cheri Mossburg contributed to this report.