CUDAHY, Wis. (AP) -- Fire crews battled a large blaze at a meatpacking plant south of Milwaukee on Monday, and authorities warned residents within a mile of the plant to leave the area because of the threat of toxic fumes.
About 100 firefighters were battling the blaze at the Patrick Cudahy Inc. plant in Cudahy, a suburb of about 18,000 residents seven miles south of downtown Milwaukee. The fire started Sunday night in an area between the sprinkler system and the roof in an area difficult to reach, Fire Chief Dan Mayer said.
Crews were working to keep it from igniting vessels containing ammonia, which is used in refrigeration, Mayer said.
"If the firewall is breached, there is the possibility of an ammonia explosion," Cudahy Mayor Ryan McCue said.
Ammonia can be extremely toxic and may be fatal if inhaled.
Carla Peterson, a plant official, said only a few of the company's roughly 2,000 workers were at the 128-year-old plant when the fire started. There were no injuries.
Three people arrived at Aurora St. Luke's South Shore hospital complaining of breathing problems, said hospital spokeswoman Myrle Croasdale. One was treated and released and the other two were being evaluated, she said.
Nearby residents were told to evacuate the area because of the threat of toxic fumes.
As of noon Monday, air quality in the neighborhood was normal, said Brian Schlieger, who was coordinating on-scene efforts for the U.S. Environmental Protection Agency.
About 200 residents, some with pets, waited out the fire at the South Milwaukee High School gymnasium Monday morning. American Red Cross workers were on hand to assist them, spokesman Maurice Robinson said.
Among those at the school was Carol Kolbe, 58, a retired home health care worker who lives three blocks from the plant. She said she saw and smelled smoke. When she heard the evacuation order she rounded up family and friends.
"I'm worried about my house and my belongings but I'm trying not to let my grandchildren see how upset I am," she said. "We're just hoping we can go back home tonight."
Dale Kordylas, 50, said his father, grandparents and great-grandfather all worked at Patrick Cudahy. He worried about whether the plant would remain open.
"How many aren't going to be called back because of this?" he asked. "That is what everybody here is worried about."
Rebecca Spencer, who lives about a quarter mile from the plant, left her home with her dog and two cats. She said she wasn't worried when she saw huge plumes of black smoke because she was confident firefighters would contain the blaze.
Nearby business also closed. About 700 employees of metal components company Ladish Co. Inc. were sent home or told not to come to work, said company vice president Larry Hammond.
Bill Otis, the chief operating officer for Patrick Cudahy, said it was too early to know the extent of the damage and what effect it might have on jobs.
The mayor declared a state of emergency so city officials could request more county and state resources.
The plant is owned by Smithfield Foods Inc., the nation's largest hog producer and pork processor. The Smithfield, Va.-based company has been restructuring its business to focus on its packaged meat business, like that done at the Cudahy plant, as it deals with weak prices for hogs and tries to recover from record high ingredient costs last year.
Associated Press writers Carrie Antlfinger and Emily Fredrix in Milwaukee contributed to this report.