Emergency teams have responded to another reported explosion in the capital of Texas - the sixth in the past three weeks.
Austin-Travis County Emergency Medical Services said a man in his 30s was injured - but police are not linking the explosion of the "incendiary device" to others which have caused panic in the city.
Investigators are continuing to pursue a suspected serial bomber terrorising Austin for weeks and have uncovered what seemed like valuable new leads in the case.
The device went off at a Goodwill store, and nearby stores and shopping centres were evacuated.
Gary Davis, president and CEO of Goodwill Texas, said the device was contained in a bag and detonated when a worker moved it.
"We put all the donations we get in a big cardboard box. He pulled something out in a bag, completely normal, and the device went off," Mr Davis said.
He added: "In this town, if an incendiary device goes off, everybody just scatters and panics. We're all on edge."
Even before the report of Tuesday evening's explosion, it had already been a busy day for authorities.
A bomb inside a package exploded around 1am on Tuesday as it passed along a conveyor belt at a FedEx shipping centre near San Antonio, causing minor injuries to a worker.
The Austin Police Department, the FBI and other federal agencies confirmed that the package centre blast was related to four previous ones that killed two people and seriously injured four others.
That explosion occurred at a FedEx facility in Schertz, just northeast of San Antonio and about 60 miles (95 kilometres) southwest of Austin.
Later in the morning, police sent a bomb squad to a FedEx facility outside the Austin airport to check on a suspicious package that was reported at around 6.20am.
Federal agencies and police later said that package had indeed contained an explosive that was successfully intercepted by authorities. They added that the intercepted package, too, was believed to be related to the other bombings.
Michael McCaul, a Republican from Austin who is chairman of the House Homeland Security Committee, said that investigators have obtained surveillance videos that "could possibly" show a suspect, but are still poring through video.
"I hope his biggest mistake was going through FedEx," Mr McCaul, who has spoken to federal investigators and Austin police Chief Brian Manley, said of the bomber.
He added that the person responsible for the bombings had previously been "very sophisticated in going around surveillance cameras".
"They've got a couple of videos that could possibly be the person but they're not sure at this point," he said.
Before it exploded, the package had been sent from Austin and was addressed to a home in Austin, Texas Attorney General Ken Paxton said.
In a statement, FedEx officials said the same person responsible for sending the package also shipped a second parcel that has been secured and turned over to law enforcement.
A company spokeswoman refused to say if that second package might have been linked to the one reported at the distribution centre near the airport.
The Schertz blast came less than two days after a bombing wounded two men Sunday night in a quiet Austin neighbourhood.
It was triggered by a nearly invisible tripwire, suggesting a "higher level of sophistication" than agents saw in three package bombs previously left on doorsteps, according to Fred Milanowski, the agent in charge of the Houston division of the Bureau of Alcohol, Tobacco, Firearms and Explosives.
Authorities have not identified the two men who were hurt in Sunday's explosion, saying only that they are in their 20s and white.
But William Grote said his grandson was one of them and that he had what appeared to be nails embedded in his knees.
On the night of the fourth bombing, one of the victims was riding a bike in the street and the other was on a sidewalk when they hit the tripwire.
"It was so dark they couldn't tell, and they tripped," Mr Grote said.
In Washington, President Donald Trump said the assailant behind the bombing is "very sick".
During an Oval Office meeting on Tuesday with Saudi Arabia's Crown Prince Mohammed bin Salman, the president said, "This is obviously a very sick individual or individuals," and authorities are "working to get to the bottom of it.