DONALDSONVILLE, La. (AP) -- An explosion and fire ripped through an ammonia processing unit at a fertilizer plant, killing one worker and injuring 10 others, five critically.

The blast Wednesday night could be felt for miles. It happened as workers cleaned an empty mixing tank at CF Industries, about 55 miles west of New Orleans in the industrial corridor along the Mississippi River.

The fire was brought under control in about 20 minutes and there were no chemical leaks, said Lt. Mike Edmonson, a state police spokesman. The plant, which makes nitrogen-based fertilizer, remained in operation except for the area involved in the explosion.

The name of the worker who died was not immediately released.

Six of the injured worked for contractors that were on the site doing routine maintenance, the company said. The other four were CF employees. Earlier counts provided by hospitals had put the number of injured at 11.

``It will obviously be some time before we know what happened, but our thoughts and prayers right now go out to the workers and their families that are involved,'' said Louis Frey, an operations manager for Long Grove, Ill.-based CF Industries.

There were 60 workers at the plant at the time of the explosion and as many as 20 near the blast site, said Doug Cain, a state police spokesman.

The cause of the explosion was not immediately known. The force of the blast, along with the fire, made it difficult to determine the exact point of explosion, Cain said.

The plant, a sprawling facility that covers more than 200 acres, is described as one of the largest nitrogen fertilizer complexes in the world.