HOUSTON >> Fire reignited today at the Houston-area industrial plant where an earlier blaze burned for days and sent plumes of black smoke over much of Southeast Texas.

Large clouds of smoke appeared before 4 p.m. today at the Intercontinental Terminals Company facility as a cleanup effort was underway at a tank that had been damaged in the earlier fire extinguished on Wednesday. Company spokesman Dale Samuelsen said the west side of the tank farm had reignited but did not say what caused the blaze.

The site continues to raise health and environmental concerns. Among the chemicals in the plant was benzene, which evaporates quickly and can cause drowsiness, dizziness, rapid heartbeat and headaches, with worse symptoms at higher levels of exposure.

A containment dike on the property breached earlier today, causing unknown chemicals and firefighting foam to spill into the nearby Houston Ship Channel and leading the U.S. Coast Guard to close the channel. The closure stopped traffic on one of the nation’s most important commercial waterways, which links refineries between the Port of Houston and the Gulf of Mexico.

As the fire burned anew, authorities also shut down a major highway bridge over the ship channel.

Crews started Tuesday trying to drain a damaged tank of flammable liquids, including benzene. An estimated 20,000 barrels of liquid were in the tank, which was one of several to catch fire originally. It wasn’t immediately clear if the damaged tank was among those that caught fire today.

Samuelsen said the company asked its neighbors, including other industrial sites and the nearby San Jacinto Texas State Historic Site, to shelter in place.

Authorities had not asked residents in surrounding Deer Park to shelter in place late this afternoon. People living near the plant in Deer Park were told Thursday to remain indoors after air monitors detected elevated levels of benzene. The order was lifted later Thursday.

Adam Adams of the Environmental Protection Agency said this morning that the other tanks that burned on site were stable.

Area schools canceled classes as testing Thursday indicated higher-than-normal levels of benzene in the air.

Adams said air tests by the EPA and the company had not shown any positive results for high levels of benzene today. One positive test after 4 a.m. from a sensor operated by Harris County was verified to be a false alarm, a county spokeswoman said.