A large plume of black smoke hovered over parts of the US city of Houston on Tuesday as firefighters struggled with a days-long chemical plant fire.
The blaze broke out Sunday at an Intercontinental Terminals Company (ITC) plant -- sending orange flames into the sky and thick black smoke wafting over the Texas city.
The plant in the suburb of Deer Park makes chemicals used in gasoline mixtures and paint thinners. The fire spread overnight from six to eight storage tanks, according to ITC.
Officials had said earlier that it could take until Wednesday for the fire to be extinguished.
But the chief executive in Harris County, where Houston is located, said there was no "specific timeline" for extinguishing the blaze.
"It's a very dynamic situation," Harris County Judge Lina Hidalgo told a news conference.
Worried residents have flooded government agencies with concerns, as they have watched black smoke spread over the region. Authorities repeatedly have assured the public that the danger was minimal.
"(The smoke) is staying high enough that the impacts on air quality right now are not high, are not measurable. We're not measuring a level that is cause for alarm," Hidalgo said.
The chemicals burning at the plant could cause coughing, difficulty breathing, irritation to the eyes, nose and throat, headaches, nausea or dizziness, according to the Harris County Public Health Department.
Officials closed nearby schools Monday, but reopened them Tuesday after air quality tests reassured officials.
"I know the cloud of black smoke seems ominous," Houston Mayor Sylvester Turner said.
"But, we want to assure everyone that the air quality is being monitored around the clock."
Turner said dozens of air monitors had been deployed around the metropolitan region, home to more than 6.3 million people.
"Air monitoring continues and as of this update readings are currently well below hazardous levels," ITC said in a statement.
"There are no injuries reported at this time."
But skeptical residents have pointed to the plume of smoke still spewing from the plant two days after the fire started.
Many parents wrote on social media that they would not send their children back to schools near the plant.
"My son's school is a couple of miles (kilometers) away. I will not gamble with his life over these false reports," one parent wrote on the Deer Park school district's Facebook page.