Its weight is equivalent to two school buses and almost a hundred feet tall -- and its metal pieces are expected to plunge back to Earth.
Officials are tracking a section of a Chinese rocket set to hit Earth on Saturday -- but they are not sure where the debris will land.
The 20-ton section of China's Long March 5B rocket is plumetting in an uncontrolled orbit at 18,000 miles per hour after blasting off last month carrying equipment of the country's new space station.
China says the upper stage of the rocket will mostly burn up on re-entry, posing very minimal threat to people and property on the ground.
Foreign Ministry representative Wang Wenbing said China "pays great attention to the re-entry of the upper stage of the rocket into the atmosphere," the South China Morning Post said.
"We're following it as closely as we can. 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," Pentagon official John Kirby said in a briefing.
While it's normal for rocket debris to fall back to Earth, this particular section has drawn concern because its lack of control means experts are not sure in what location it will plunge.
China's space agency has yet to confirm whether the main stage of the massive Long March rocket is being controlled or will make an uncontrolled re-entry.
Last May, another Chinese rocket fell uncontrolled into the Atlantic Ocean off West Africa, CBC News said.
"We don't have a plan to shoot the rocket down. We're hopeful that it will land in a place where it won't harm anyone," U.S. Defence Secretary Lloyd Austin said in remarks quoted by SCMP.