China's defunct Tiangong 1 space station hurtled toward Earth on Sunday and was expected to re-enter the atmosphere within hours.
Most of the craft should burn up on re-entry, so scientists said falling debris poses only a slight risk to people on the ground.
The European Space Agency forecast that the station, whose name translates as "Heavenly Palace," will re-enter sometime between Sunday night and early Monday GMT. The Chinese space agency said it should happen during the course of Monday Beijing time.
The Aerospace Corp. predicted Tiangong 1's re-entry would take place within 2 hours of either side of 0018 GMT Monday (8:18 p.m. Sunday EDT.)
Based on the space station's orbit, it will come back to Earth somewhere 43 degrees north and 43 degrees south, a range covering most of the United States, China, Africa, southern Europe, Australia and South America. Out of range are Russia, Canada and northern Europe.
Only about 10 percent of the bus-sized, 8.5-ton spacecraft will likely survive being burned up on re-entry, mainly its heavier components such as its engines. The chances of any one person being hit by debris are considered less than one in a trillion.
Launched in 2011, Tiangong 1 was China's first space station, serving as an experimental platform for bigger projects, such as the Tiangong 2 launched in September 2016 and a future permanent Chinese space station.
The station played host to two crewed missions and served as a test platform for perfecting docking procedures and other operations. Its last crew departed in 2013 and contact with it was cut in 2016.
Since then, it has orbited gradually closer and closer to Earth on its own while being monitored.
Many Western space experts think China has lost control of the station. China's chief space laboratory designer, Zhu Zongpeng, has denied Tiangong was out of control, but hasn't provided specifics on what, if anything, China was doing to guide the craft's return to Earth.