The core stage from the Long March-5b vehicle was used to launch the first module of China's new space station last month. But the return of the rocket stage will be uncontrolled, and at 18 tonnes it is one of the largest items in decades to have an undirected dive into the atmosphere.

Various space debris modelling experts are pointing to the early hours (GMT) of Sunday as the likely moment of re-entry. However, such projections are always highly uncertain.

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