There were no immediate reports of injuries or evacuations in the largely commercial and industrial area located in southwestern Illinois, officials said.
At least three fire departments were on the scene, with at least two others on standby, according to officials.
Firefighters were pumping water out of small nearby reservoirs, and rains that rolled into the area also helped extinguish small grass fires.
A company spokeswoman told area television stations that crews were working to block all incoming valves, cutting off flammables that could feed the fire.
``We have experienced, trained personnel who know how to fight fires with the products that come into this terminal,'' Melissa Erker said. ``The most important thing is that the crews extinguish this fire safely.''
Erker said the company had fire crews on the scene and had summoned people from its Wood River refinery to assist.
She declined to speculate when the fire might be extinguished.
Erker said the blaze broke out about 6:15 a.m. after lightning hit the pumping station at the site, rupturing a propane pipeline and sparking the fire.
Cahokia is about six miles southwest of St. Louis.
