CROCKETT, Calif. (AP) — A fire raging at a fuel storage facility in the San Francisco Bay Area prompted a hazardous materials emergency Tuesday afternoon that led authorities to order about 12,000 people in two communities to stay inside with all windows and doors closed.

Emergency sirens blared and thick plumes of black smoke and flames filled the skyline around the NuStar Energy LP facility in Crockett, California, about 30 miles (50 kilometers) northeast of San Francisco.

“This is a very dynamic, rapidly evolving situation,” Capt. George Laing of the Contra Costa Fire Department said. He said authorities received numerous reports of explosions before the fire and that the flaming tanks “are releasing chemicals that are still burning.”

Initially, authorities reported that two storage tanks were on fire from the blaze that started just before 2 p.m. But 90 minutes later said the blaze had spread to an additional tank, leading to several nearby grass fires.

“We have three large storage tanks burning in the facility behind me,” Contra Costa Fire Department spokesman Steve Hill said at a late afternoon news conference. He said the tanks held varying amounts of ethanol, including one that contained about 167,000 gallons of ethanol.

About 200 firefighters were battling the blazes, using foam on the flames and water to cool the adjacent tanks at the facility, Hill said.

A resident of Rodeo, Gabriel Iturbe, sat in bumper-to-bumper traffic as he tried to get home to his teenage son, who was home sick when he called his father to report a loud explosion.

“It literally rocked the house and then soon after, he heard what sounded like a jet plane,” Iturbe said, speaking from his cellphone in the car as he looked at “thick, black smoke.” He said he was trying to reach his son and take him out to a less smoky location.

In a statement, NuStar Energy said that the company was cooling nearby tanks to minimize the spread of fire but provided few other details. The company is a fuel storage and pipeline operator based in San Antonio, Texas.

The Contra Costa Health Department posted on Twitter that there was a “hazardous materials emergency” in the towns of Crockett, home to about 3,100 people, and Rodeo, population 8,700. The department urged residents to stay inside and close all windows and doors.

“Cover any cracks around doors or windows with tape or damp towels. Stay off the phone unless you need to report a life-threatening emergency at your location,” the department said.

The city of Vallejo also tweeted that its residents should stay inside.

Officials closed Interstate 80 in both directions, one of the busiest in the Bay Area, causing massive backups at the height of evening rush hour.

Officials said they did not immediately know the cause of the fire and whether there was any connection to a 4.5-magnitude earthquake Monday night centered in the East Bay city of Pleasant Hill, north of Oakland.

That quake caused malfunctions at two nearby oil refineries operated by Shell and Marathon oil, Randy Sawyer, Contra Costa County’s chief environmental health and hazardous materials officer, told KQED News. Some equipment at the Shell refinery was temporarily affected by the quake, spokesman Ray Fisher said.

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