GREELEY, Colo. -- A flat tank near a drilling rig exploded in a flash fire in near Greeley in Weld County Wednesday morning, injuring three people.

The incident happened near North 83rd Avenue and F Street around 7:30 a.m.

Weld County spokeswoman Margie Martinez said vapors from the tank were ignited by the hot catalytic converter on the exhaust of a pickup truck that pulled up, carrying workers.

"The two employes were burned on their face and taken by ground transport to North Colorado Medical Center." said Martinez.

A third worker suffered minor burns and was treated at the scene, she said.

The open-topped flat tank contained a "cocktail" of petroleum products, according to Union Colony Fire Chief Dale Lyman. He said the drilling rig was not involved in the fire.

Judy Firestien, who lives about a mile to the north of the explosion, told 7NEWS that she was getting out of bed when she heard the explosion. She said she looked out her window and saw a large ball of flame rising into the air.

A woman, who identified herself as Bev, lives across the street from the site told KOA Radio that she heard "a loud bang" when the tank went up in flames.

A large plume of black smoke from the fire was visible for miles. Windsor Fire was called in to assist Union Colony Fire.

The tank farm is owned by Eastern Colorado Well Service, according to Martinez.