Editor's Note: A toxic cloud that formed after 300 gallons of hydrochloric acid leaked at a plant in southeast Texas sent nine people to the hospital and forced thousands of residents to stay indoors for a few hours. Here is the story.

The following were the developments as they came in:

[Updated at 8:47 a.m.] The stay-indoors order has been lifted, according to the Texas City Emergency Management office. Roads that were closed in the south of the city also have been reopened, CNN affiliate KTRK reports.

[Updated at 6:35 a.m.] Officials say they expect to lift the stay-indoors order at 6 a.m. local time (7 a.m. ET).

[Updated at 4:53 a.m.] None of those exposed to the chemical have life-threatening injuries, KTRK reports.

It's not the first time the more than 45,000 residents of Texas City have dealt with a threat from a chemical leak. In March, an acid leak was reported at BP's refinery in the port city. And last year, several dozen homes were evacuated when 250,000 gallons of gasoline spilled following a pipeline rupture.

[Updated at 4:38 a.m.] Right now, city officials are trying to clean up the leak that occurred when a tank at the plant ruptured, Clawson told CNN affiliate

KTRK. Officials hope to lift the order to stay inside by about 3 a.m. local time.

It wasn't immediately known what the chemical was being used for at the plant. Hydrochloric acid has a number of industrial uses. It also has a corrosive effect on human tissue, with the potential to damage the lungs, eyes, skin, and intestines.

[Updated at 4:19 a.m.] The leak occurred at the Dallas Group of America’s plant near the Port of Texas City, Bruce Clawson of the Emergency Management office said. The toxic cloud has covered portions of the port and possibly southern parts of the city that sits along the coast of Galveston Bay, he said.

Of those who were hospitalized for exposure, four were firefighters, according to Clawson.

[Posted at 4:05 a.m.] At least nine people have been hospitalized after being exposed to a toxic cloud that formed after 300 gallons of hydrochloric acid leaked in Texas City, according to the Texas City Emergency Management office.

Residents in the city are being asked to remain indoors, turn off air conditioning units and make sure all windows and doors are closed until the vapor cloud dissipates.