The craft is expected to re-enter in an area around 40.4 degrees west, 27.4 degrees south, the authority said on its website, giving it a position off the coast to the southwest of Rio de Janeiro and Sao Paulo.

Beijing said at the weekend that it was unlikely any large pieces would reach the ground.

The 10.4m-long Tiangong-1, or Heavenly Palace 1, was launched in 2011 to carry out docking and orbit experiments as part of China's ambitious space programme, which aims to place a permanent station in orbit by 2023.

It was originally planned to be decommissioned in 2013 but its mission was repeatedly extended.

China had said its re-entry would occur in late 2017 but that process was delayed, leading some experts to suggest the space laboratory is out of control.

The Chinese tabloid Global Times said today that worldwide media hype about the re-entry reflected overseas "envy" of China's space industry.

"It's normal for spacecraft to re-enter the atmosphere, yet Tiangong-1 received so much attention partly because some Western countries are trying to hype and sling mud at China's fast-growing aerospace industry," it said.

Only about 10 per cent of the bus-sized, 8.5-tonne spacecraft was expected to not be burned up on re-entry - mainly its heavier components such as its engines. The chances of any one being hit by debris are considered less than one in a trillion.