A storage tank containing chemicals at a factory in the city of Garden Grove, south of Los Angeles, overheated on Thursday. The tank is now at risk of rupture, which could lead to the chemicals leaking onto the ground or causing an explosion.
The tank has been emitting toxic fumes since Thursday.
"It's going to break, and we don't know when. We're doing our best to figure out when or how we can prevent it," said Fire Chief Craig Covey.
An evacuation order was first issued to residents in Garden Grove, but was later expanded to include some residents in five nearby cities.
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