(CNN) -- About 500 people were evacuated and a portion of I-44 closed early Monday as St. Louis firefighters battled a five-alarm chemical fire, the city's fire chief said.
Three firefighters suffered minor injuries, Chief Dennis Jenkerson said.
The fire at Chemisphere Corp.'s west St. Louis storage yard involved tankers, rail cars and other storage tanks containing solvents, Jenkerson said. A Fire Department spokeswoman said the solvents were acetone and ethanol.
The fire was under control as of about 6 a.m. CT. But when firefighters arrived at about 2:30 a.m., "We had the whole yard going," Jenkerson said.
Because the materials were highly flammable and the heated storage tanks were at risk of exploding, police evacuated a three-block radius around the plant, Jenkerson said.
"We expected the worst," Jenkerson said. "We kept it from going that far."
He said fire crews were making sure all of the storage tanks were cool and that none were leaking before allowing residents to return.
Jenkerson said he was unsure when I-44 would reopen. Fire crews were using part of the highway, which sits above the fire site, as a staging area.
It's too early to say what started the fire, Jenkerson said.
Chemisphere was founded in 1976 as a solvent distribution company, but now is also engaged in the manufacture of personal care products such as ethanol-based hand sanitizers, industrial products and other materials, according to its website.
It can store up to 1.1 million gallons of chemicals at the site, according to the website.