A piece of Chinese spacecraft is due to plunge to Earth sometime between tonight and Sunday evening, the European Space Agency has said.
The Tiangong-1 (Heavenly Palace 1), which is about the size of a bus, was sent into orbit in 2011 for experiments as part of China's space programme.
It had been set for a controlled re-entry into Earth's atmosphere.
But it stopped working in March 2016 – three years after it was last occupied – and there is no way of knowing where it will land.
Without being able to communicate with the space lab, Earth-based controllers have no way of firing its engines or thrusters and no way of controlling its descent.
The craft is about 120 miles from Earth, down from about 185 miles in January, according to the European Space Agency.
Previous estimates showed Tiangong-1's re-entry into the atmosphere would be on 1 April (Easter Sunday) or three days either side of that date.
The ESA revised the estimate due to a number of factors, including calmer weather than expected. But the estimate was still "highly variable", it warned.
Researchers had said that a number of the spacecraft's parts – including its dense rocket engines – would be unlikely to burn up, leaving chunks of the craft to crash towards the planet's surface.
They fear that debris could survive the atmosphere and land anywhere 43 degrees either side of the equator.
The China Manned Space Engineering Office said on its WeChat social media account that falling spacecraft do "not crash into the Earth fiercely like in sci-fi movies, but turn into a splendid (meteor shower) and move across the beautiful starry sky as they race towards the Earth".
They said the atmospheric drag would tear away the external components of the craft when it gets to an altitude of around 60 miles.
The heat will grow and friction will cause the main structure of the lab to burn or blow up, with most of the parts dissolving in the air.
Some of the debris will fall slowly before landing, most likely in the ocean, the Chinese predicted.
The ESA said nearly 6,000 uncontrolled re-entries of large objects have occurred over the past 60 years without anyone being hurt.
More from China
China's foreign ministry spokesman Lu Kang said: "I want to highlight that we attach importance to this issue and we've been dealing with it very responsibly in accordance with relevant laws and regulations.
"If there is a need, we will promptly be in touch with the relevant country."