Chinese rocket debris expected to plunge toward Earth

Officials are tracking a section of a Chinese rocket expected to plunge down to Earth as early as Saturday -- but they aren't sure where it will land.

"It's too soon to know exactly where it's going to come down," Pentagon spokesperson John Kirby said in a briefing Wednesday.

The section is part of a rocket called Chinese Long March 5B, which launched a module of the country's first permanent space station into orbit last week.

"We're tracking it, we're following it as closely as we can," Kirby said. "It's just a little too soon right now to know where it's going to go or what, if anything, can be done about that."

The U.S. Space Command confirmed it was "aware of and tracking" the location of the rocket, but said "its exact entry point into the Earth's atmosphere cannot be pinpointed until within hours of its reentry." The Federal Aviation Administration said it's "engaged" with NORAD "and will send out an advisory to any facilities that would be potentially affected."

"Tactical decisions, if needed, will be made based on real-time information," the FAA said.

According to Aerospace.org, a nonprofit that performs technical analyses and assessments for a variety of government, civil and commercial customers, the current orbital inclination "means that reentry can be as far north as Chicago, New York City, Rome and Beijing and as south as New Zealand and Chile."

"That places any of those locations within the potential reentry path of this giant piece of space junk measuring 98 feet long and 16.5 feet wide and weighs 21 metric tons," the group said.

Typically, rockets that plunge back to Earth are brought back in a controlled way into the ocean. One expert said it's unclear why this rocket's return to Earth is uncontrolled.

"I heard speculation that that they intended it to be controlled and something broke. Stuff goes wrong in space. Space is hard," Ted Muelhaupt, principal director of Aerospace's Center for Orbital Reentry and Debris Studies, said in an interview with ABC News.

The Chinese government has yet to comment publicly on the rocket's reentry, according to the Associated Press.

"If something's going to reenter and there's a risk of more than one in 10,000, then it could cause injury to a person," Muelhaupt said. "Then you take steps to mitigate that. And the most common way to do it is to control where the vehicle lands. Essentially, you bring the vehicle down where people are not."

ABC News' Lizann Robinson contributed to this report.